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All questions of Linear Equations for ACT Exam

The solution of equation 10x + 26 = 0 is a / an________.
  • a)
    Rational Number
  • b)
    Irrational Number
  • c)
    Negative integer
  • d)
    Positive integer
Correct answer is option 'A'. Can you explain this answer?

Ayesha Joshi answered
Given:
The given equation is 10x + 26 = 0
Concept:
Rational numbers are the numbers that can be written in the form of p/q, where q is not equal to zero. 
Calculation:
10x + 26 = 0
⇒ 10x = -26
⇒ x = (-26)/10
⇒ x = -13/5
∴ 10x + 26 = 0 is a rational number.

In a group of 1300 students, every student reads 5 subjects and every subject is read by 65 students. The number of subjects are:
  • a)
    exactly 100
  • b)
    may be 250
  • c)
    at the most 70
  • d)
    at least 10
Correct answer is option 'A'. Can you explain this answer?

Amelia Green answered
Understanding the Problem
In a scenario with 1300 students, each reading 5 subjects, and each subject read by 65 students, we need to determine the number of subjects available.
Data Breakdown
- Total students (S) = 1300
- Subjects read per student (P) = 5
- Students per subject (N) = 65
Total Subject Readings Calculation
To find the total number of subject readings, we multiply the number of students by the number of subjects each student reads:
- Total readings = S × P
- Total readings = 1300 × 5 = 6500
Finding the Number of Subjects
We know that each subject is read by 65 students, so we can express the total readings in terms of the number of subjects (T):
- Total readings = T × N
- 6500 = T × 65
Now, we can solve for T:
- T = 6500 / 65
- T = 100
Conclusion
The calculations indicate that the number of subjects is exactly 100. Thus, the correct answer is option 'A'.
Analysis of Other Options
- May be 250: This is incorrect because it would imply more readings than available.
- At most 70: This contradicts our calculation.
- At least 10: While this is true, it does not represent the exact number.
Therefore, the only viable option based on the calculations is option 'A', which confirms that there are exactly 100 subjects.

The difference between two numbers is 5. If 25 is subtracted from the smaller number and 20 is added to the greater number the ratio becomes 1 : 2. What is the greater number?
  • a)
    80
  • b)
    90
  • c)
    85
  • d)
    75
Correct answer is option 'A'. Can you explain this answer?

Layla Rivera answered
Understanding the Problem
We have two numbers, which we can denote as x (greater number) and y (smaller number).
Key Conditions
- The difference between the two numbers is 5:
- x - y = 5
- If 25 is subtracted from the smaller number and 20 is added to the greater number, the ratio of the two becomes 1:2:
- (y - 25) / (x + 20) = 1 / 2
Setting Up Equations
1. From the first condition:
- x = y + 5
2. Substituting x in the second condition:
- (y - 25) / ((y + 5) + 20) = 1 / 2
- This simplifies to (y - 25) / (y + 25) = 1 / 2
Cross-Multiplying
Cross-multiplying gives us:
- 2(y - 25) = 1(y + 25)
This expands to:
- 2y - 50 = y + 25
Solving for y
Rearranging the equation:
- 2y - y = 25 + 50
- y = 75
Finding the Greater Number
Using the relationship x = y + 5:
- x = 75 + 5
- x = 80
Conclusion
The greater number is 80.
Thus, the correct answer is option 'A'.

The cost of one dozen bananas is Rs. 5. The cost of one dozen oranges is Rs. 75. What will the cost of one and a quarter dozen bananas and three-fourth dozen oranges?
  • a)
    Rs. 112.50
  • b)
    Rs. 131.25
  • c)
    Rs. 62.50
  • d)
    Rs. 93.75
Correct answer is option 'C'. Can you explain this answer?

Rajeev Kumar answered
The cost of one dozen bananas = Rs. 5
One and a quarter dozen means 12 + 1/4 × 12 = 15
So, cost of one and a quarter dozen bananas = 15 × 5/12 = Rs. 6.25
The cost of one dozen oranges = Rs. 75
So, cost of three-fourth dozen oranges = 12 × 3/4 × 75/12 = Rs. 56.25
So, total cost = 6.25 + 56.25 = Rs. 62.50

Consider a matrix  
The matrix A satisfies the equation 6A-1 = A2 + cA + dI, where c and d are scalars and I is the identity matrix. Then (c + d) is equal to
  • a)
    5
  • b)
    17
  • c)
    -6
  • d)
    11
Correct answer is option 'A'. Can you explain this answer?

Orion Classes answered
Concept:
for the given square matrix, the characteristic equation will be
|B - AI| = 0
B = Given matrix
I = Unit matrix
A = Characteristic roots
Calculation:
|B - AI| = 0
Take the determinant of matrix, then 
(1 - A) [(4 - A) (1 - A) + 2] = 0
(1 - A) [4 - 4A - A + A2 + 2] = 0
(1 - A) [4 - 5A + A2 + 2] = 0
(1 - A) [A2 - 5A + 6] = 0
A2 - 5A + 6 - A3 + 5A2 - 6A = 0
-A3 + 6A2 - 11A + 6 = 0
A3 - 6A2 + 11A = 6
A2 - 6A + 11 = 6A-1       ........(1)
Given 6A-1 = A2 + cA + dI     .........(2)
Compare 1 and 2
c = -6, d = +11
c + d = +5

Find x:
  • a)
    3
  • b)
    4
  • c)
    5
  • d)
    1
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered
⇒ -22x – 26 = 8 - 56x
⇒ 56x - 22x = 26 + 8
⇒ 34x = 34
∴ x = 1

If x2 - 7x + 1 = 0 then find the value of (x + 1/x).
  • a)
    3
  • b)
    7
  • c)
    -7
  • d)
    -3
Correct answer is option 'B'. Can you explain this answer?

Ayesha Joshi answered
Given:
x2 - 7x + 1 = 0
Calculation:
x2 - 7x + 1 = 0
Dividing by x:
⇒ x - 7 + 1/x = 0
⇒ x + 1/x = 7
∴ Value of x + 1/x = 7 

If the equations 14x + 8y + 5 = 0 and 21x - ky - 7 = 0 have no solution, then the value of k is:
  • a)
    12
  • b)
    -12
  • c)
    8
  • d)
    -16
Correct answer is option 'B'. Can you explain this answer?

Quantronics answered
⇒ The equations have no solution when their slopes are same
⇒ Slope of equation 1 = - 14/8 = - 7/4
⇒ Slope of equation 2 = 21/k
⇒ So, 21/k = - 7/4
∴ The value of k is - 12.

If 50 is subtracted from two-third of a number, the result is equal to sum of 40 and one-fourth of that number. What is the number?
  • a)
    136
  • b)
    199
  • c)
    176
  • d)
    216
Correct answer is option 'D'. Can you explain this answer?

Henry Foster answered
To solve this problem, let's assume the number we're trying to find is represented by the variable 'x'.

Let's break down the information given in the problem:

1. "Two-thirds of a number" can be represented as (2/3) * x.
2. "50 is subtracted from two-thirds of a number" can be written as (2/3) * x - 50.
3. "One-fourth of that number" can be represented as (1/4) * x.
4. "The result is equal to the sum of 40 and one-fourth of that number" can be written as (1/4) * x + 40.

So, the equation becomes:

(2/3) * x - 50 = (1/4) * x + 40

To simplify the equation, we can multiply it by the least common denominator, which is 12. This will eliminate the fractions:

12 * [(2/3) * x - 50] = 12 * [(1/4) * x + 40]

8x - 600 = 3x + 480

Next, let's isolate the variable 'x' by moving the constant terms to one side and the variable terms to the other side of the equation:

8x - 3x = 480 + 600

5x = 1080

Now, divide both sides of the equation by 5 to solve for 'x':

x = 1080 / 5

x = 216

Therefore, the number we were looking for is 216, which corresponds to option 'D'.

If x6 + x5 + x4 + x3 + x2 + x + 1 = 0, then find the value of x5054 + x6055 - 7
  • a)
    9
  • b)
    5
  • c)
    -9
  • d)
    -5
Correct answer is option 'D'. Can you explain this answer?

Ayesha Joshi answered
Given:
x6 + x5 + x4 + x3 + x2 + x + 1 = 0
Calculation:
Considering the given equation
x6 + x5 + x4 + x3 + x2 + x + 1 = 0      -----(1)
In equation (1) multiplying by x
x7 + x6 + x5 + x4 + x3 + x2 + x = 0      -----(2)
Equation (2) – (1)
⇒ x7 - 1 = 0
⇒ x7 = 1
x5054 + x6055 - 7
⇒ (x7)722 + (x7)865 – 7
⇒ (1)722 + (1)865 – 7
⇒ 1 + 1 – 7
⇒ - 5
∴ Required value is – 5

For what value of k, the system linear equation has no solution
(3k + 1)x + 3y - 2 = 0
(k2 + 1)x + (k - 2)y - 5 = 0
  • a)
    1
  • b)
    -1
  • c)
    2
  • d)
    6
Correct answer is option 'B'. Can you explain this answer?

Ayesha Joshi answered
Given:
a1 = 3k + 1
b1 = 3
c1 = -2
a2 = k2 + 1
b2 = k - 2
c2 = -5
Formula Used:

Calculation: 
By cross multiplication
⇒ (3k + 1)(k - 2) = 3(k2 + 1)
⇒ 3k2 - 6k + k - 2 = 3k2 + 3
⇒ -5k - 2 = 3
⇒ -5k = 5
∴ k = -1 
The correct option is 2 i.e. -1

Difference of two numbers is 50% of the smaller number. If greater number is 120, then find sum of both numbers is:
  • a)
    250
  • b)
    220
  • c)
    200
  • d)
    150
Correct answer is option 'C'. Can you explain this answer?

Ayesha Joshi answered
Given:
Greater number = 120
Calculation:
Let smaller number be x
According to the question
120 – x = x × (50/100)
⇒ 120 – x = x/2
⇒ 240 – 2x = x
⇒ x + 2x = 240
⇒ 3x = 240
⇒ x = 240/3
⇒ x = 80
∴ Sum of both numbers = 120 + 80 = 200

Cost of 8 pencils, 5 pens and 3 erasers is Rs. 111. Cost of 9 pencils, 6 pens and 5 erasers is Rs. 130. Cost of 16 pencils, 11 pens and 3 erasers is Rs. 221. What is the cost (in Rs) of 39 pencils, 26 pens and 13 erasers?
  • a)
    316
  • b)
    546
  • c)
    624
  • d)
    482
Correct answer is option 'B'. Can you explain this answer?

Rajeev Kumar answered
Let the price of single pencil, pen, and eraser be x, y, and z respectively
According to question,
8x + 5y + 3z = Rs. 111      ----(1)
9x + 6y + 5z = Rs. 130      ----(2)
16x + 11y + 3z = Rs. 221      ----(3)
Subtracting equation (1) from (3)
⇒ (16x + 11y + 3z) - (8x + 5y + 3z) = 221 - 111
⇒ 8x + 6y = 110
⇒ 4x + 3y = 55      ----(4)
Multiply the equation (2) by 3 and (3) by 5 and then subtracting equation (2) from (3)
⇒ (16x + 11y + 3z) × 5 - (9x + 6y + 5z) × 3 = 221 × 5 - 130 × 3
⇒ 80x + 55y + 15z - 27x - 18y - 15z = 1105 - 390
⇒ 53x + 37y = 715      ----(5)
Multiply the equation (4) by 53 and (5) by 4 and then subtracting equation (4) from (5)
⇒ 212x + 159y - 212x - 148y = 2915 - 2860
⇒ 11y = 55
⇒ y = 5
By putting the value of y = 5 in equation (4)
⇒ 4x + 3 × 5 = 55
⇒ x = 10
By putting the value of y = 5 and x = 10 in equation (1)
⇒ 8 × 10 + 5 × 5 + 3z = 111
⇒ 80 + 25 + 3z = 111
⇒ z = 2
∴ Cost of 39 pencils, 26 pens and 13 erasers is 39x + 26y + 13z = 39 × 10 + 26 × 5 + 13 × 2 = Rs. 546
Shortcut Trick
Let, price of 1 pencil = x, price of 1 pen = y and price of one eraser = z
Then, 8x + 5y + 3z = 111      ----(1)
9x + 6y + 5z = 130      ----(2)
16x + 11y + 3z = 221      ----(3)
Adding (1), (2) and (3), we get
33x + 22y + 11z = 462
⇒ 3x + 2y + z = 42
⇒ 39x + 26y + 13z = 546      (multiplying with 13) 

The sum of three consecutive number is 126. Find the highest number?
  • a)
    41
  • b)
    42
  • c)
    43
  • d)
    44
Correct answer is option 'C'. Can you explain this answer?

Lila Williams answered
Step-by-Step Solution:

Let's assume the three consecutive numbers are x, x+1, and x+2.

1. Write the equation based on the given information:
- x + (x+1) + (x+2) = 126

2. Combine like terms and solve for x:
- 3x + 3 = 126
- 3x = 123
- x = 41

3. Find the highest number:
- x+2 = 41 + 2 = 43
Therefore, the highest number among the three consecutive numbers is 43, which corresponds to option C.

A total of 324 notes comprising of Rs. 20 and Rs. 50 denominations make a sum of Rs. 12450. The number of Rs. 20 notes is
  • a)
    200
  • b)
    144
  • c)
    125
  • d)
    110
Correct answer is option 'C'. Can you explain this answer?

Ayesha Joshi answered
Given:
Total number of notes of Rs. 20 and Rs. 50 = 324
Total Sum = Rs. 12450
Concept used:
Value of note × Number of total notes = Total amount
Calculation:
Let the number of Rs. 20 notes be x.
No. of Rs. 50 notes = 324 – x
⇒ 20 × x + 50 × (324 – x) = 12450 
⇒ 20x + 16200 – 50x = 12450
⇒ -30x = 12450 – 16200
⇒ 30x = 3750
⇒ x = 125
∴ The number of Rs. 20 notes is 125. 

For what value of λ, do the simultaneous equation 2x + 3y = 1, 4x + 6y = λ have infinite solutions?
  • a)
    λ = 0 
  • b)
    λ = 1
  • c)
    λ ≠ 2
  • d)
    λ = 2
Correct answer is option 'D'. Can you explain this answer?

Orion Classes answered
Concept:
Non-homogeneous equation of type AX = B has infinite solutions;
if ρ(A | B) = ρ(A) < Number of unknowns
Calculation:
Given:
2x + 3y = 1
4x + 6y = λ
The augmented matrix is given by:
For the system to have infinite solutions, the last row must be a fully zero row.
So if λ = 2 then the system of equations has infinitely many solutions.
Key Points:
Remember the system of equations
AX = B have
1. Unique solution, if ρ(A : B) = ρ(A) = Number of unknowns.
2. Infinite many solutions, if ρ(A : B) = ρ(A) < Number of solutions
3. No solution, if ρ(A : B) ≠ ρ(A).

If the sum and product of two numbers is 34 and 288 respectively, find the sum of their cubes.
  • a)
    9236
  • b)
    9928
  • c)
    9854
  • d)
    8352
Correct answer is option 'B'. Can you explain this answer?

Owen Foster answered
Let's assume the two numbers as x and y.
We are given that the sum of the two numbers is 34, so we can write the equation as:
x + y = 34 ...(1)

We are also given that the product of the two numbers is 288, so we can write the equation as:
xy = 288 ...(2)

To find the sum of their cubes, we need to find the values of x and y first.

Solving the equations:
From equation (1), we can express y in terms of x:
y = 34 - x

Substituting this value of y in equation (2), we get:
x(34 - x) = 288

Expanding the equation:
34x - x^2 = 288

Rearranging the equation:
x^2 - 34x + 288 = 0

Now we can solve this quadratic equation to find the values of x.

Factoring the equation:
(x - 16)(x - 18) = 0

Setting each factor equal to zero:
x - 16 = 0 or x - 18 = 0

Solving for x, we have two possible solutions:
x = 16 or x = 18

Now we can find the corresponding values of y:
For x = 16, y = 34 - 16 = 18
For x = 18, y = 34 - 18 = 16

So the two numbers are 16 and 18.

Finding the sum of their cubes:
16^3 + 18^3 = 4096 + 5832 = 9928

Hence, the sum of their cubes is 9928, which corresponds to option (b).

Rajeev was to earn Rs. 500 and a free holiday for seven weeks’ work. He worked for only 5 weeks and earned Rs. 50 and a free holiday. What was the value of the holiday?
  • a)
    Rs. 1,075
  • b)
    Rs. 1,850
  • c)
    Rs. 1,550
  • d)
    Rs. 1,675
Correct answer is option 'A'. Can you explain this answer?

To earn Rs. 500 and a free holiday for seven weeks, Rajeev must meet certain conditions or complete certain tasks. These conditions or tasks were not mentioned in the question, so it is not possible to determine how Rajeev can achieve this goal without further information.

Jane won a lottery and gets 1/3rd of the winning amount and donates Rs. 6000 which is 1/6th  of amount he got, find how much the lottery was worth.
  • a)
    36000
  • b)
    18000
  • c)
    54000
  • d)
    108000
Correct answer is option 'D'. Can you explain this answer?

Given Information:
Jane won a lottery and gets 1/3rd of the winning amount and donates Rs. 6000 which is 1/6th of the amount he got.

Calculations:
Let the total amount of the lottery be x.
1. Jane gets 1/3 of the winning amount:
Amount Jane gets = 1/3 * x
2. Jane donates Rs. 6000, which is 1/6th of the amount she got:
1/6 * (1/3 * x) = 6000
3. Solve for x:
1/18 * x = 6000
x = 6000 * 18
x = 108000
Therefore, the lottery was worth Rs. 108000.
Therefore, the correct answer is option D) 108000.

A man has equal number of five, ten and twenty rupee notes amounting to Rs. 385. Find the total number of notes?
  • a)
    13
  • b)
    33
  • c)
    15
  • d)
    31
Correct answer is option 'B'. Can you explain this answer?

Ayesha Joshi answered
Given:
Number of Five rupee note = Number of Ten rupee note = Number of Twenty rupee note
Calculation:
Let the equal number of five, ten and twenty rupee notes be x
⇒ 5x + 10x + 20x = 385
⇒ 35x = 385
⇒ x = 385/35 = 11
Total number of notes = 11 notes of Rs 5 + 11 notes of Rs 10 + 11 Rs of 20 =  33 notes
Check:
11 notes of Rs 5 + 11 notes of Rs 10 + 11 Rs of 20 = 11 × 5 + 11 × 10 + 11 × 20 = 55 + 110 + 220 = Rs. 385
Total number of notes = 11 × 3 = 33 
Therefore the correct answer is 33.
Alternate Method:
Since the number of Rs 5, Rs 10, and Rs 20 notes are equal, the ratio of the number of notes is = 1 ∶ 1 ∶ 1
Or, we can say, the total number of notes must be multiple of 3.
 Only two options are multiple of 3, others can be eliminated.
option 2 : 33. That means the number of notes of each dimension is 33/3 = 11.
5 × 11 + 11 × 10 + 11 × 20 = 385
∴ The total number of notes is 33.

If 8k6 + 15k3 – 2 = 0, then the positive value ofis:
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A'. Can you explain this answer?

Quantronics answered
Given:
8k6 + 15k3 – 2 = 0
Calculation:
Let, k3 = x
So, 8x2 + 15x - 2 = 0
⇒ 8x2 + 16x - x - 2 = 0
⇒ 8x (x + 2) - 1 (x + 2) = 0
⇒ (8x - 1) (x + 2) = 0
⇒ 8x - 1 = 0 ⇒ x = 1/8
⇒ x + 2 = 0 ⇒ x = - 2 [Not posiible because of negative value]
Now, k= 1/8
⇒ k = 1/2 ⇒ 1/k = 2
Then, (k + 1/k) = (1/2 + 2) = 5/2 = 
∴ The value of (k + 1/k) is 

The value of k for which the system of equations x + ky + 3z = 0, 4x + 3y + kz = 0, 2x + y + 2z = 0 has non-trivial solution is
  • a)
    k = 0 or 9/2
  • b)
    k = 10
  • c)
    k < 9
  • d)
    k > 0
Correct answer is option 'A'. Can you explain this answer?

Orion Classes answered
Concept:
Consider the system of m linear equations
a11 x1 + a12 x2 + … + a1n xn = 0
a21 x1 + a22 x2 + … + a2n xn = 0
am1 x1 + am2 x2 + … + amn xn = 0
  • The above equations containing the n unknowns x1, x2, …, xn. To determine whether the above system of equations is consistent or not, we need to find the rank of the following matrix.
  • A is the coefficient matrix of the given system of equations.
  • Where, Ax, Ay, Az is the coefficient matrix of the given system of equations after replacing the first, second, and third columns from the constant term column which will be having all the entries as 0.
  • In the case of homogeneous equations, the determinants of, Ax, Ay, Az will be 0 definitely.
  • So, for the system of homogeneous equations having the the-trivial solution, the determinant of A should be zero.
  • The system of homogeneous equations has a unique solution (trivial solution) if and only if the determinant of A is non-zero.
Calculation:
For non - trivial solution, the |A| = 0
⇒ 1(6 - K) - K(8 - 2K) + 3(4 - 6) = 0
⇒ 9K -  2K2 = 0
⇒ k = 0 or 9/2

If 80% of my age 6 years ago is the same as 60% of my age after 10 years. What is the product of digits of my present age?
  • a)
    24
  • b)
    20
  • c)
    30
  • d)
    15
Correct answer is option 'B'. Can you explain this answer?

Let's assume the present age as 'x'.

Given that 80% of the age 6 years ago is the same as 60% of the age after 10 years, we can write the equation as:

0.8(x - 6) = 0.6(x + 10)

Simplifying this equation:

0.8x - 4.8 = 0.6x + 6

Subtracting 0.6x from both sides:

0.2x - 4.8 = 6

Adding 4.8 to both sides:

0.2x = 10.8

Dividing both sides by 0.2:

x = 54

Therefore, the present age is 54.

To find the product of the digits of the present age, we can multiply the digits together:

Product = 5 * 4 = 20

Hence, the product of the digits of the present age is 20, which corresponds to option B.

Find the value of p for which the system of linear equations: px - 3y = 5 and 6x + 2y = 12 has no solutions?
  • a)
    8
  • b)
    7
  • c)
    4
  • d)
    -9
Correct answer is option 'D'. Can you explain this answer?

Rajeev Kumar answered
The given system of equations is of the form:
⇒ a1x + b1y + c1 = 0
⇒ a2x + b2y + c2 = 0
Here, a1 = p; b1 = -3; c= -5; a2 = 6; b2 = 2; c2 = -12
For no solution
⇒ a1/a2 = b1/b2 ≠ c1/c2
⇒ p/6 = -3/2
⇒ p = (-3/2) × 6
⇒ p = -9
∴ The value of p is -9

For what value of μ do the simultaneous equations 5x + 7y = 2, 15x + 21y = μ have no solution?
  • a)
    μ = 0
  • b)
    μ ≠ 6
  • c)
    μ ≠ 0
  • d)
    μ = 6
Correct answer is option 'B'. Can you explain this answer?

Ayesha Joshi answered
Concept:
System of equations
a1x + b1y = c1
a2x + b2y = c2
For unique solution

For Infinite solution

For no solution
Calculation:
Given:
5x + 7y = 2, 15x + 21y = μ
Here For no solution

Hence for no solution μ ≠ 6

A piece of cloth costs Rs. 35. If the piece were 4 m longer and each meter was to cost Rs. 1 lesser, then the total cost would remain unchanged. How long is the piece of cloth?
A. 10 m
B. 14 m
C. 12 m
D. 8 m
  • a)
    B
  • b)
    D
  • c)
    C
  • d)
    A
Correct answer is option 'A'. Can you explain this answer?

Rajeev Kumar answered
Let, length of the piece of cloth = x m
Cost of cloth = Rs. 35
∴ Cost of 1 m cloth = Rs. 35/x
According to the question,
⇒ (x + 4) (35/x - 1) = 35
⇒ 35 - x + 140/x - 4 = 35
⇒ 35x - x2 + 140 - 4x = 35x
⇒ x2 + 4x - 140 = 0
⇒ x2 + 14x - 10x - 140 = 0
⇒ x(x + 14) - 10(x + 14) = 0
⇒ (x + 14) (x - 10) = 0
⇒ x = - 14 or 10
∴ The piece of cloth is 10 m long
Alternate Method:
We can tabulate the given data according to the following table:


As the total remains constant at Rs.35, we get:
xy = 35     
⇒ x = 35/y      ----(i)
Also, (x – 1) × (y + 4) = 35      ----(ii)
On substituting the value of x from equation (i) into equation (ii), we get:
[(35/y) – 1] × (y + 4) = 35 
On solving, we get:
y = -14 and 10
∴ The piece of cloth is 10 m long

The system of linear equations 
-y + z = 0
(4d - 1) x + y + Z = 0
(4d - 1) z = 0 
has a non-trivial solution, if d equals 
  • a)
    1/2
  • b)
    1/4
  • c)
    3/4
  • d)
    1
Correct answer is option 'B'. Can you explain this answer?

Ayesha Joshi answered
Concept

For a homogeneous system of linear equations:
Having non-trivial solution:
The rank of the matrix should be less than the number of variables.
Or determinant of the matrix should be equal to zero.
Calculation:
Given:
-y + z = 0
(4d - 1) x + y + Z = 0
(4d - 1) z = 0
For non-trivial solution:
det. A = 0
⇒ |A| = 0
⇒ 0 × [(4d - 1) - 0] + 1 × [(4d - 1)2 - 0] + 1(0 - 0) = 0
⇒ (4d - 1)2 = 0

∴ The system of linear equations has a non-trivial solution if d equals to 1/4

A set of linear equations is given in the form Ax = b, where A is a 2 × 4 matrix with real number entries and b ≠ 0. Will it be possible to solve for x and obtain a unique solution by multiplying both left and right sides of the equation by AT (the super script T denotes the transpose) and inverting the matrix AT A?
  • a)
    Yes, it is always possible to get a unique solution for any 2 × 4 matrix A.
  • b)
    No, it is not possible to get a unique solution for any 2 × 4 matrix A.
  • c)
    Yes, can obtain a unique solution provided the matrix AT A is well conditioned
  • d)
    Yes, can obtain a unique solution provided the matrix A is well conditioned.
Correct answer is option 'B'. Can you explain this answer?

Gabriel Rivera answered
X2 matrix, x is a column vector of variables, and b is a column vector of constants. The linear equations can be written as:

a11x1 + a12x2 = b1
a21x1 + a22x2 = b2

where a11, a12, a21, a22 are the elements of matrix A, and x1, x2 are the variables.

This system of equations can be solved using various methods, such as substitution, elimination, or matrix inversion. The solution, if it exists, will be a unique solution, no solution, or infinitely many solutions depending on the coefficients and constants in the equations.

The sum of two numbers is 184. If one-third of one exceeds one-seventh of the other by 8,  find the smaller number
  • a)
    92
  • b)
    84
  • c)
    72
  • d)
    76
Correct answer is option 'C'. Can you explain this answer?

Rajeev Kumar answered
Given:
The sum of two numbers = 184
Calculation:
Let the numbers be x and (184 − x)
According to the question,
x × (1/3) - (184 − x)/7 = 8
⇒ (7x - 552 + 3x)/21 = 8
⇒ 7x - 552 + 3x = 8 × 21
⇒ 10x = 168 + 552
⇒ x = 720/10 = 72
One number = 72
Other number = 184 − x = 184 - 72 = 112
∴ The smaller number is 72.

The ratio of the number of blue and red balls in a bag is constant. When there were 68 red balls, the number of blue balls was 36. If the number of blue balls was 63, how many red balls should be there in the bag?
  • a)
    98
  • b)
    119
  • c)
    102
  • d)
    110
Correct answer is option 'B'. Can you explain this answer?

Aiden Powell answered
Given:
- The ratio of the number of blue and red balls in a bag is constant.
- When there were 68 red balls, the number of blue balls was 36.

To find:
- The number of red balls when there are 63 blue balls.

Solution:
Let's assume the constant ratio of blue to red balls is 'x'.

Using the given information:
- When there were 68 red balls, the number of blue balls was 36.
- This can be represented as 36/x = 68.
- Solving this equation, we find x = 68/36 = 17/9.

Calculating the number of red balls when there are 63 blue balls:
- We know that the ratio of blue to red balls is constant at 17/9.
- Let the number of red balls be 'r'.
- We can set up the equation (63/17) = (r/9) to represent the ratio.
- Solving this equation, we find r = (63*9)/17 = 33.

Therefore, when there are 63 blue balls, there should be 33 red balls in the bag.

The approximate solution of the system of simultaneous equations
2x - 5y + 3z = 7
x + 4y - 2z = 3
2x + 3y + z = 2
by applying Gauss-Seidel method one time (using initial approximation as x - 0, y - 0, z - 0) will be:
  • a)
    x = 2.32, y = 1.245, z = -3.157
  • b)
    x = 1.25, y = -2.573, z = -3.135
  • c)
    x = 2.45, y = -1.725, z = -3.565
  • d)
    x = 3.5, y = -0.125, z = -4.625
Correct answer is option 'D'. Can you explain this answer?

Ayesha Joshi answered
Gauss Seidel Method:
In Gauss Seidel method, the value of x calculated is used in next calculation putting other variable as 0.
2x - 5y + 3z = 7
Putting y = 0, z = 0 ⇒ x = 3.5
x + 4y - 2z = 3
Putting x = 3.5, z = 0 ⇒ y = - 0.125
2x + 3y + z = 2
Putting x = 3.5, y = - 0.125 ⇒ z = 2 – 3(-0.125) – 2(3.5)
z = - 4.625

If  then which one of the following is correct?
  • a)
    A3 - 3A2 - 4A + 11I = 0
  • b)
    A3 - 4A2 - 3A + 11I = 0
  • c)
    A3 + 4A2 - 3A + 11I = 0
  • d)
    A3 - 3A2 + 4A + 11I = 0
Correct answer is option 'B'. Can you explain this answer?

Ayesha Joshi answered
(1 - λ) (-3λ + λ2 + 2) - 3(6 - 2λ + 1) + 2(4 + λ) = 0
(1 - λ) (λ2 - 3λ + 2) - 3(7 - 2λ) + 2(4 + λ) = 0
λ3 - 4λ2 - 3λ + 11 = 0
By C-H theorem replace λ by A
A3 - 4A2 - 3A + 11I = 0

The cost of 7 chairs, 2 tables and 5 fans is Rs. 9350. If the cost of 3 chairs and a fan is Rs. 1950, find the cost of 2 chairs, 1 table and 2 fans.
  • a)
    Rs. 2500
  • b)
    Rs. 2725
  • c)
    Rs. 3050
  • d)
    Rs. 3700
Correct answer is option 'D'. Can you explain this answer?

To find the cost of 2 chairs, 1 table, and 2 fans, we can use the given information to set up a system of equations and solve for the unknown values.

Let's assume the cost of a chair is x, the cost of a table is y, and the cost of a fan is z.

1) Cost of 7 chairs, 2 tables, and 5 fans is Rs. 9350:
7x + 2y + 5z = 9350

2) Cost of 3 chairs and a fan is Rs. 1950:
3x + z = 1950

Now we have a system of two equations with three unknowns. To solve this system, we need to eliminate one variable.

Multiplying equation 2 by 5, we get:
15x + 5z = 9750

Now we can subtract equation 1 from equation 3 to eliminate z:
(15x + 5z) - (7x + 2y + 5z) = 9750 - 9350
8x - 2y = 400

Now we have two equations with two unknowns:
7x + 2y + 5z = 9350
8x - 2y = 400

Solving these equations, we can find the values of x and y.

Multiplying equation 2 by 4, we get:
32x - 8y = 1600

Adding equation 4 to equation 1, we eliminate y:
(7x + 2y + 5z) + (32x - 8y) = 9350 + 1600
39x + 5z = 10950

We can solve this equation together with equation 3 to find the values of x and z.

Multiplying equation 3 by 5, we get:
35x + 5z = 9750

Now we can subtract equation 5 from equation 6 to eliminate z:
(39x + 5z) - (35x + 5z) = 10950 - 9750
4x = 1200
x = 300

Substituting the value of x back into equation 3, we can find the value of z:
3x + z = 1950
3(300) + z = 1950
900 + z = 1950
z = 1050

Now that we have the values of x and z, we can substitute them into equation 1 to find the value of y:
7x + 2y + 5z = 9350
7(300) + 2y + 5(1050) = 9350
2100 + 2y + 5250 = 9350
2y + 7350 = 9350
2y = 2000
y = 1000

Therefore, the cost of 2 chairs, 1 table, and 2 fans is:
2x + y + 2z = 2(300) + 1000 + 2(1050) = 600 + 1000 + 2100 = Rs. 3700

Hence, the correct answer is option 'D', Rs. 3700.

Three cups of ice cream, two burgers and four soft drinks together cost Rs. 128. Two cups of ice cream, one burger and two soft drinks together cost Rs. 74. What is the cost of five burgers and ten soft drinks?
  • a)
    Rs. 160
  • b)
    Rs. 128
  • c)
    Rs. 170
  • d)
    Cannot be determined
Correct answer is option 'C'. Can you explain this answer?

Rajeev Kumar answered
Let cost of each ice cream, burger and soft drink is x, y and z respectively.
3x + 2y + 4z = 128      ---- (i)
2x + y + 2z = 74      ---- (ii)
Multiply 3 × (ii) and 2 × (i), we get
6x + 3y + 6z = 222      ----(iii)
6x + 4y + 8z = 256      ----(iv)
substract equation (iv) to equation (iii)
y + 2z = 34
Multiply the above equation by 5 
we get,
5 (y + 2z) = 5 × 34
5y + 10z = 170 
∴ cost of 5 burgers and 10 soft drinks = 34 × 5 = 170

If 1/3rd of the first of the three consecutive odd numbers is 2 more than 1/5th of the third number, then the second number is?
  • a)
    21
  • b)
    23
  • c)
    25
  • d)
    19
Correct answer is option 'B'. Can you explain this answer?

Avery Martin answered
To solve this problem, let's assume the first odd number as x.

First Odd Number: x
Second Odd Number: x + 2 (since the numbers are consecutive odd numbers)
Third Odd Number: x + 4 (since the numbers are consecutive odd numbers)

According to the given information:
1/3rd of the first number is 2 more than 1/5th of the third number.

Mathematically, this can be represented as:

1/3 * x = (1/5 * (x + 4)) + 2

Now, let's solve this equation step by step.

Step 1: Simplify the equation

1/3 * x = 1/5 * (x + 4) + 2

Step 2: Multiply both sides of the equation by the least common multiple (LCM) of 3 and 5, which is 15, to eliminate the fractions.

15 * (1/3 * x) = 15 * (1/5 * (x + 4) + 2)

5x = 3(x + 4) + 30

Step 3: Distribute on the right side of the equation

5x = 3x + 12 + 30

Step 4: Combine like terms

5x = 3x + 42

Step 5: Subtract 3x from both sides of the equation

5x - 3x = 42

2x = 42

Step 6: Divide both sides of the equation by 2

x = 42/2

x = 21

Now that we have the value of x, we can find the second number by adding 2 to the first number.

Second Odd Number = x + 2 = 21 + 2 = 23

Therefore, the second number is 23, which matches with option B.

If the system
2x – y + 3z = 2
x + y + 2z = 2
5x – y + az = b
Has infinitely many solutions, then the values of a and b, respectively, are
  • a)
    – 8 and 6
  • b)
    8 and 6
  • c)
    – 8 and –6
  • d)
    8 and –6
Correct answer is option 'B'. Can you explain this answer?

Ayesha Joshi answered
Concept:
Consider the system of m linear equations
a11 x1 + a12 x2 + … + a1n xn = b1
a21 x1 + a22 x2 + … + a2n xn = b2
am1 x1 + am2 x2 + … + amn xn = bm
The above equations containing the n unknowns x1, x2, …, xn. To determine whether the above system of equations is consistent or not, we need to find the rank of following matrices.
A is the coefficient matrix and [A|B] is called as augmented matrix of the given system of equations.
We can find the consistency of the given system of equations as follows:
  • If the rank of matrix A is equal to the rank of augmented matrix and it is equal to the number of unknowns, then the system is consistent and there is a unique solution, i.e.
    Rank of A = Rank of augmented matrix = n
  • If the rank of matrix A is equal to the rank of augmented matrix and it is less than the number of unknowns, then the system is consistent and there are an infinite number of solutions.
    Rank of A = Rank of augmented matrix < n
  • If the rank of matrix A is not equal to the rank of the augmented matrix, then the system is inconsistent, and it has no solution.
    Rank of A ≠ Rank of augmented matrix
Calculation:
Given linear system is
2x – y + 3z = 2
x + y + 2z = 2
5x – y + az = b
Then augmented matrix form is written below;
For rank (A) < n = 3
‘a’ must be = 8
For rank [A|B] < 3, b = 6
Therefore a = 8 & b = 6

If y2 = y + 7, then what is the value of y3?
  • a)
    8y + 7
  • b)
    y + 14
  • c)
    y + 2
  • d)
    4y + 7
Correct answer is option 'A'. Can you explain this answer?

Given: y^2 = y - 7

To find: The value of y^3

Solution:
To find the value of y^3, we need to multiply y^2 by y.

y^2 * y = (y - 7) * y

Expanding the equation:

y^3 = y * y - 7 * y

Simplifying further:

y^3 = y^2 - 7y

But we already know that y^2 = y - 7.

Substituting this value into the equation:

y^3 = (y - 7) - 7y

Simplifying again:

y^3 = y - 7 - 7y

Combining like terms:

y^3 = -6y - 7

Therefore, the value of y^3 is -6y - 7.

Answer:
The correct option is (A) 8y - 7.

3 chairs and 2 tables cost Rs. 700 and 5 chairs and 3 tables cost Rs. 1100. What is the cost of 1 chair and 2 tables?
  • a)
    Rs. 350
  • b)
    Rs. 400
  • c)
    Rs. 500
  • d)
    Rs. 550
Correct answer is option 'C'. Can you explain this answer?

Rajeev Kumar answered
Given:
3 chairs and 2 tables cost Rs. 700
5 chairs and 3 tables cost Rs. 1100
Calculation:
Let the cost of 1 chair be Rs. x and 1 table be Rs. y
Now, According to the question
3x + 2y = 700      ----(1)
5x + 3y = 1100      ----(2)
By solving (1) and (2), we get 
x = 100 and y = 200
Now, we have to find the cost of 1 chair and 2 tables
∴ x + 2y = 100 + 400 = Rs. 500

Gauss-Seidel method is used to solve the following equations (as per the given order):
x1 + 2x2 + 3x3 = 5
2x1 + 3x2 + x3 = 1
3x1 + 2x2 + x3 = 3
Assuming initial guess as x1 = x2 = x3 = 0, the value of x3 after the first iteration is ________
    Correct answer is '-6'. Can you explain this answer?

    Ayesha Joshi answered
    Gauss Seidel Method:
    In Gauss Seidel method, the value of x calculated is used in next calculation putting other variable as 0.
    x1 + 2x2 + 3x3 = 5
    Putting x2 = 0, x3 = 0 ⇒ x1 = 5
    2x1 + 3x2 + x3 = 1
    Putting x1 = 5, x3 = 0 ⇒ x2 = -3
    3x1 + 2x2 + x3 = 3
    Putting x1 = 5, x2 = -3 ⇒ x3 = 3 – 3(5) – 2 (-3)
    x3 = 3 – 15 + 6
    x3 = -6
    Mistake Point: Don’t arrange them diagonally because It is given in question solve as per given order.

    In a group of 100 students, every student study 8 subjects and every subject is studied by 10 students. The number of subjects is:
    • a)
      Exactly 80
    • b)
      May be 50
    • c)
      At most 30
    • d)
      At least 90
    Correct answer is option 'A'. Can you explain this answer?

    Orion Classes answered
    Total students = 100
    According to the question
    Every students study 8 subjects, then total subjects = 8 × 100 = 800
    If every subject is studied by 10 students, then number of subjects = 800/10 = 80

    A is 5 years older than B and 10 years younger than C. If the sum of ages of A, B and C together after 5 years is 80 years. Find the present age of B.
    • a)
      15 years
    • b)
      20 years
    • c)
      30 years
    • d)
      25 years
    Correct answer is option 'A'. Can you explain this answer?

    Mila Mitchell answered
    Given information:
    - A is 5 years older than B
    - A is 10 years younger than C
    - The sum of ages of A, B, and C together after 5 years is 80 years

    Let's assume the present age of B as x.

    Age of A:
    Since A is 5 years older than B, the present age of A would be x + 5.

    Age of C:
    Since A is 10 years younger than C, the present age of C would be (x + 5) + 10 = x + 15.

    Sum of ages after 5 years:
    After 5 years, the age of A will be (x + 5) + 5 = x + 10.
    After 5 years, the age of B will be x + 5.
    After 5 years, the age of C will be (x + 15) + 5 = x + 20.

    According to the given information, the sum of ages of A, B, and C after 5 years is 80 years:

    (x + 10) + (x + 5) + (x + 20) = 80
    3x + 35 = 80
    3x = 45
    x = 15

    Therefore, the present age of B is 15 years.

    Consider matrix  The number of distinct real values of k for which the equation Ax = 0 has infinitely many solution is________
      Correct answer is '2'. Can you explain this answer?

      Orion Classes answered
      Concept:
      We can find the consistency of the given system of equations as follows:
      (i) If the rank of matrix A is equal to the rank of an augmented matrix and it is equal to the number of unknowns, then the system is consistent and there is a unique solution.
      The rank of A = Rank of augmented matrix = n
      (ii) If the rank of matrix A is equal to the rank of an augmented matrix and it is less than the number of unknowns, then the system is consistent and there are an infinite number of solutions.
      The rank of A = Rank of augmented matrix < n
      Then |A| = 0
      (iii) If the rank of matrix A is not equal to the rank of the augmented matrix, then the system is inconsistent, and it has no solution.
      The rank of A ≠ Rank of an augmented matrix
      Application:
      A system to have infinitely many solutions must satisfy:
      |A| = 0
      K(K – 2(K – 1) = 0
      K(K – 2K + 2) = 0
      K(-K + 2) = 0
      K = 0, 0, 2
      Hence, there are 3 eigen values, and two distinct eigen value and 1 repeated eigen value.

      Consider the system of equations  The value of x3 (round off to the nearest integer), is ______.
        Correct answer is '3'. Can you explain this answer?

        Ayesha Joshi answered
        The given system has 4 equations and 3 unknowns.
        Hence it is a over-determined system of equations.
        The equations are;
        x1 + 3x2 + 2x3 = 1       --(1)
        2x1 + 2x2 - 3x3 = 1     ---(2)
        4x1 + 4x2 - 6x3 = 2     ---(3)
        2x1 + 5x2 + 2x3 = 1     ---(4)
        Note that equation (2) and (3) are linearly dependent on each other and equation 3 is twice that of equation (2).
        Hence considering equation 1, 2 and 4 -



        ⇒ x3 = 3
        Important Points:
        • Under-determined system: Number of equations < Number of unknowns
        • Over-Determined system: Number of equation > Number of unknowns
        • Equally Determined system: Number of equation = Number of unknowns

        If the system of equations 2x + 3y = 5, 4x + ky = 10 has infinitely many solutions then k =?
        • a)
          6
        • b)
          4
        • c)
          3
        • d)
          2
        Correct answer is option 'A'. Can you explain this answer?

        Kennedy Martin answered
        Given:
        The system of equations is:
        1) 2x + 3y = 5
        2) 4x + ky = 10

        To Find:
        The value of k if the system of equations has infinitely many solutions.

        Solution:
        To determine if the system of equations has infinitely many solutions, we need to check if the two equations are dependent or independent.

        1. Dependent Equations:
        If the two equations are dependent, it means that one equation is a multiple of the other. In this case, there will be infinitely many solutions.

        2. Independent Equations:
        If the two equations are independent, it means that they intersect at a single point, and there is a unique solution.

        Method:
        To check if the equations are dependent or independent, we can compare the slopes of the equations.

        Equation 1: 2x + 3y = 5
        Rewriting it in slope-intercept form:
        3y = -2x + 5
        y = (-2/3)x + 5/3

        Equation 2: 4x + ky = 10
        Rewriting it in slope-intercept form:
        ky = -4x + 10
        y = (-4/k)x + 10/k

        Comparing the Slopes:
        The slopes of the two equations are -2/3 and -4/k. To have infinitely many solutions, the slopes must be equal.

        Therefore, we can equate the slopes:
        -2/3 = -4/k

        Solving for k:
        To solve for k, we can cross-multiply:
        -2k = -12

        Divide both sides by -2:
        k = 6

        So, the value of k for which the system of equations has infinitely many solutions is 6 (option A).

        A woman had only 50 paisa and 1 rupee coins in her purse. The total number of coins were 120 and the total amount was Rs.100. So the number of 1 rupee coins are_______.
        • a)
          60
        • b)
          70
        • c)
          80
        • d)
          90
        Correct answer is option 'C'. Can you explain this answer?

        Mason Hicks answered
        The given problem involves finding the number of 1 rupee coins in a woman's purse based on the total number of coins and the total amount in the purse. Let's break down the problem step by step to find the answer.

        Given information:
        - Total number of coins: 120
        - Total amount in the purse: Rs. 100

        Let's assume the number of 50 paisa coins as 'x' and the number of 1 rupee coins as 'y'.

        1. Set up equations:
        - The total number of coins equation: x + y = 120
        - The total amount equation: (0.50 * x) + (1 * y) = 100

        2. Simplify the equations:
        - x + y = 120
        - 0.50x + y = 100

        3. Solve the equations using substitution or elimination method:
        We can multiply the first equation by 0.50 to make the coefficients of 'y' the same in both equations:
        0.50(x + y) = 0.50(120)
        0.50x + 0.50y = 60

        Subtract the second equation from the above equation:
        (0.50x + y) - (0.50x + 0.50y) = 100 - 60
        0.50x + y - 0.50x - 0.50y = 40
        0.50y - 0.50y = 40
        0.50y - 0.50y = 0

        4. Simplify the equation:
        0 = 40

        This is not possible as it results in an inconsistency. It means that our assumption for the number of 50 paisa coins and 1 rupee coins is incorrect. Let's reassess the problem.

        Let's assume the number of 1 rupee coins as 'x' and the number of 50 paisa coins as 'y'.

        1. Set up equations:
        - The total number of coins equation: x + y = 120
        - The total amount equation: (1 * x) + (0.50 * y) = 100

        2. Simplify the equations:
        - x + y = 120
        - x + 0.50y = 100

        3. Solve the equations using substitution or elimination method:
        We can multiply the first equation by 0.50 to make the coefficients of 'y' the same in both equations:
        0.50(x + y) = 0.50(120)
        0.50x + 0.50y = 60

        Subtract the second equation from the above equation:
        (x + 0.50y) - (0.50x + 0.50y) = 100 - 60
        x + 0.50y - 0.50x - 0.50y = 40
        x - 0.50x = 40
        0.50x - 0.50x = 0

        4. Simplify the equation:
        0 = 40

        Again, this is not possible as it results in an inconsistency. It means that our second assumption for the number of 1 rupee coins and 50 paisa coins is also incorrect. Let's reassess the problem once again.

        Let's assume the number of 1 rupee coins as 'x'

        If (a + b)– 2(a + b) = 80 and ab = 16, then what can be the value of 3a – 19b?
        • a)
          -16
        • b)
          -14
        • c)
          -18
        • d)
          -20
        Correct answer is option 'B'. Can you explain this answer?

        Rajeev Kumar answered
        (a + b)– 2(a + b) = 80
        ⇒ (a + b)– 2(a + b) + 1 = 81
        ⇒ (a + b – 1)2 = 81
        ⇒ a + b – 1 = 9
        ⇒ a + b = 10
        given ab = 16
        ⇒ a = 8 and b = 2
        ⇒ 3a – 19b = 24 – 38 = -14

        If (x + 6y) = 8, and xy = 2, where x > 0, what is the value of (x3 + 216y3)?
        • a)
          470
        • b)
          368
        • c)
          224
        • d)
          288
        Correct answer is option 'C'. Can you explain this answer?

        The question seems to be incomplete. We need more information about the variable "x" in order to solve the equation.

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