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CSIR NET Mathematical Science Mock Test - 2 - UGC NET MCQ


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30 Questions MCQ Test CSIR NET Exam Mock Test Series 2025 - CSIR NET Mathematical Science Mock Test - 2

CSIR NET Mathematical Science Mock Test - 2 for UGC NET 2025 is part of CSIR NET Exam Mock Test Series 2025 preparation. The CSIR NET Mathematical Science Mock Test - 2 questions and answers have been prepared according to the UGC NET exam syllabus.The CSIR NET Mathematical Science Mock Test - 2 MCQs are made for UGC NET 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for CSIR NET Mathematical Science Mock Test - 2 below.
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CSIR NET Mathematical Science Mock Test - 2 - Question 1

A ranks 10th from both the top and the bottom in merit among the girls in her class. B ranks 6th from the top and 16th from the bottom among boys in the same class. If A is immediately ahead of B in merit order, her rank in the entire class would be

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 1

Given:
A ranks 10th from both the top and the bottom in merit among the girls in her class. B ranks 6th from the top and 16th from the bottom among boys in the same class.

Concept:
Apply concept of sitting arrangement .

Calculation:
A ranks 10th from both the top and the bottom in merit among the girls in her class.
Then total girls in class = 10 +10 -1 = 19
B ranks 6
th from the top and 16th from the bottom among boys in the same class.
Then total boys in class = 6 + 16 - 1 = 21
Hence the total students in the class = 19 + 21 = 40

If A is immediately ahead of B in merit order,
Then Before A 9 girls and 5 boys in class then Rank of A from the top is 15 and the rank of A from the bottom is 40 -15 +1 = 26

Hence the option (2) is correct.

CSIR NET Mathematical Science Mock Test - 2 - Question 2

Standard deviations for first 10 natural numbers is

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 2

Formula used:

1. Sum of the first n natural numbers =

2. Sum of the square of the first n natural numbers =

3. Standard deviation,

Calculation:

The first n natural numbers are 1,2,3,.....,n.

Their mean, x̅ = ∑x/n​ = (1 + 2 + 3 +.....+ n)/n

⇒ [n(n + 1)/2n]

⇒ (n + 1)/2

Again,

Sum of the square of the first n natural numbers is ∑x2 = [n(n + 1)(2n + 1)/6]

Their mean = ∑x2/n = [n(n + 1)(2n + 1)/6n]

⇒ [(n + 1)(2n + 1)/6]

Now,

Now putting n = 10,

So, the standard deviations for the first 10 natural numbers

≈ 2.87

∴ The standard deviation for the first 10 natural numbers is 2.87.

CSIR NET Mathematical Science Mock Test - 2 - Question 3

The sum of digits of a two-digit number is 12. When the digits are interchanged, the resulting number is 36 more than original number. What is the original two-digit number ?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 3

Given:

Sum of digits of two-digit number = 12

Calculation:

Let the tens place and unit place digits of the two-digit number be x and y respectively.

Therefore original number =

According to question

From equation (1) and (2)

∴Tthe original two-digit number is 48.

Hence, 48 is the correct answer.

CSIR NET Mathematical Science Mock Test - 2 - Question 4

What would be the minimum number of notes for Rs 4849 if notes are available only in denominations of Rs 2, 5, 20, 50, 500?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 4

Rs. 4849 ÷ 500 = 9 remainder 349.
So, we use 9 Rs. 500 notes, leaving us with Rs. 349 to be accounted for.

Rs. 349 ÷ 50 = 6 remainder 49.
So, we use 6 Rs. 50 notes, leaving us with Rs. 49 to be accounted for.

Rs. 49 ÷ 20 = 2 remainder 9.
So, we use 2 Rs. 20 notes, leaving us with Rs. 9 to be accounted for.

Rs. 9 ÷ 5 = 1 remainder 4.
So, we use 1 Rs. 5 note, leaving us with Rs. 4 to be accounted for.

Rs. 4 ÷ 2 = 2.
So, we use 2 Rs. 2 notes.

Total number of notes used
9 notes of Rs. 500, 6 notes of Rs. 50, 2 notes of Rs. 20, 1 note of Rs. 5 and 2 notes of Rs. 2

Total = 9 + 6 + 2 + 1 + 2 = 20 notes

Thus, the minimum number of notes required is Option 2) .

CSIR NET Mathematical Science Mock Test - 2 - Question 5

An athlete running on a track falls short of the finish line by 10 m when she runs at a constant speed for a given time. If she increases her speed by 20%, she overshoots by 20 m in the same time. What is the length of the track?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 5

Concept:
The fundamental formula for motion is, Distance = Speed × Time

Explanation:
Let d be the length of the track (what we are trying to find), v be her normal speed and t be the time she runs.
At normal speed, the distance covered is d - 10, so so v⋅t = d − 10(Equation 1)
When she increases her speed by 20%, her new speed is 1.2v , and she covers a distance of d + 20, so:

Hence, the correct option is 3).

CSIR NET Mathematical Science Mock Test - 2 - Question 6

The son was born when his mother was 28 years old. The father is older to the mother by 4 years. If the current ages of the father and mother are in the ratio 9 : 8, what is the current age (in years) of the son?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 6

The son was born when the mother was 28 years old, the father is 4 years older than the mother, the current ages of the father and mother are in the ratio 9:8. We need to find the current age of the son.
Let the current age of the mother be 8x years.
Then, the current age of the father will be 9x years (since their ages are in the ratio of 9:8).
From the problem, we know the father is 4 years older than the mother. Therefore,
9x = 8x + 4
⇒ x = 4 ​​
Mother’s current age = 8x = 8 × 4 = 32 years.
Father’s current age = 9x = 9 × 4 = 36  years.
The son was born when the mother was 28 years old. The mother is currently 32 years old.
The son is currently 4 years old, so the correct answer is Option 3).

CSIR NET Mathematical Science Mock Test - 2 - Question 7
A person takes loan of Rs. 1,50,000 at a compound interest rate of 10% per annum. If the loan is repaid at the end of the 3rd year, what is the total interest paid?
Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 7

Concept:

Let P be the principle, r be the rate of interest, n be the time compounded annually then amount A = P(1+)n

Explanation:

Here P = 1,50,000, n = 3, r = 10

So A = 150000(1 + )3 = 150000(1 + 0.1)3 = 150000(1.1)3 = 199650

Therefore total interest = A - P = 199650 - 150000 = 49650

Option (4) is correct

CSIR NET Mathematical Science Mock Test - 2 - Question 8
The standard deviation of data x1, x2, x3, …, xn is σ(σ > 0). Then the standard deviation of data 3x1 + 2, 3x2 + 2, 3x3 + 2, …, 3xn + 2 is
Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 8

Concept:

(i) Standard deviation of n data x1, x2, x3, …, xn of mean μ is

SD =

(ii) The Standard Deviation of a set remains unchanged if each data is increased or decreased by a constant however changes similarly when data is multiplied or divided by a constant. i.e., SD(ax + b) = a SD(x)

Explanation:

The standard deviation of data x1, x2, x3, …, xn is σ

So using the above concept, standard deviation of data 3x1 + 2, 3x2 + 2, 3x3 + 2, …, 3xn + 2 is

3 × (standard deviation of data x1, x2, x3, …, xn) = 3σ

Option (1) is correct

CSIR NET Mathematical Science Mock Test - 2 - Question 9

From a two-digit number, the sum of its digits is subtracted. The resulting number is

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 9

Let ab be a two digit number.
So, we can write ab = 10 a + b
Now, sum of digits of Two - digit number ab is a+b
⇒ 10a + b - (a+b) = 10a + b - a - b = 9a
Hence, Clearly we can see 9a is always divisible by 9
Hence, Option (B) is true

CSIR NET Mathematical Science Mock Test - 2 - Question 10
Let A be a 4 × 4 matrix with determinant 60 and two eigenvalues are 1 + 2i and 3. Which of the following is the trace of A
Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 10

Concept:

(i) Trace of a square matrix is equal to the sum of the eigenvalues.

(ii) Determinant of a square matrix is equal to the product of the eigenvalues.

Explanation:

A is 4 × 4 matrix

Two eigenvalues are 1 + 2i and 3, so 3rd eigenvalue will be 1 - 2i.

Let 4th eigenvalue be λ

det(A) = product of eigenvalues

⇒ (1 + 2i)(1 - 2i) × 3 × λ = 60

⇒ 5 × 3 × λ = 60

⇒ λ = 4

So, trace of eigenvalues = 1 + 2i + 1 - 2i + 3 + 4 = 9

(2) is true.

CSIR NET Mathematical Science Mock Test - 2 - Question 11

Let f(x) be a polynomial of unknown degree taking the values

All the fourth divided differences are. -1/6. Then the coefficient of x3 is

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 11

f(x) is a polynomial of unknown degree taking the values

All the fourth divided differences are. -1/6.

Divide difference table is

Then polynomial is

f(x) = f(x0) + (x - x0)Δf(x0) + (x -x0)(x - x12f(x0) + (x -x0)(x - x1)(x - x23f(x0) + (x -x0)(x - x1)(x - x2)(x - x34f(x0)
= 2 + (x - 0)(x - 1) × 5 + (x - 0)(x - 1) × 1/2 + (x - 0)(x - 1)(x - 2) + (x - 0)(x - 1)(x - 2)(x - 3)

Therefore the coefficient of x3 is = 1/3

Option (1) is true

CSIR NET Mathematical Science Mock Test - 2 - Question 12
At z = 0 the function f(z) = exp() has
Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 12

Concept:

A complex function f(z) has

(i) a removal singularity at z = a if exist

(ii) a pole of order m at z = a if ≠ 0

(iii) an essential singularity at z = a if does not exist

Explanation:

f(z) = exp()

= (0/0 form)

Using L'hospital rule

= , does not exist

Hence f(z) has an essential singularity at z = 0

(3) is correct

CSIR NET Mathematical Science Mock Test - 2 - Question 13

Let be i.i.d.(independent and identically distributed) random variables with uniform distribution on the interval [0, 1]. Let denote the kth order statistic based on the sample . If we select two different samples of size 25 and 26, denoted asand respectively, and let Y be the 8th order statistic in both samples. What is the probability that ?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 13

The probability that Y25,8 = Y26,8 is 0. The reason is that Y25,8 and Y26,8  are each defined at different points on the [0, 1] interval, as they are based on different samples. Since the random variables X1,X2,...,Xn  are independently and identically distributed, it is extremely unlikely (indeed, with probability 0) that such an equality would occur.

Hence option (i) is correct.

CSIR NET Mathematical Science Mock Test - 2 - Question 14

Let {Xn |n ≥ 0} be a homogeneous Markov chain with state space S = {0, 1, 2, 3, 4} and transition probability matrix

Let α denote the probability that starting with state 4 the chain will eventually get absorbed in closed class {0, 3}. Then the value of α is

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 14

We label by ai the probability that, starting in state i, the chain is eventually absorbed in the closed set {0,3}. Since {0,3} is closed,

  • a₀ = 1 (if you start in 0 you’re already in {0,3}),

  • a₃ = 1,
    and the other closed state 1 lies outside our target class, so

  • a₁ = 0.

States 2 and 4 are transient, and satisfy the usual linear equations
a₂ = P(2→0)·a₀ + P(2→1)·a₁
a₄ = Σₖ P(4→k)·aₖ.

From the matrix row for state 2, P(2→0)=1/3, P(2→1)=2/3, and no chance to go directly to 3 or 4. Hence
a₂ = (1/3)·1 + (2/3)·0 = 1/3.

From the row for state 4, the transitions are

  • to 0 with probability 1/8,

  • to 1 with probability 1/8,

  • to 2 with probability 1/2,

  • to 3 with probability 1/8,

  • to 4 itself with probability 1/8.

Thus
a₄ = (1/8)·a₀ + (1/8)·a₁ + (1/2)·a₂ + (1/8)·a₃ + (1/8)·a₄
Substitute a₀=1, a₁=0, a₂=1/3, a₃=1:
a₄ = 1/8 + 0 + (1/2)·(1/3) + 1/8 + (1/8)·a₄
a₄ = 1/8 + 1/6 + 1/8 + (1/8)a₄
Combine the constants: 1/8+1/8 =1/4, and 1/4+1/6 = (3/12+2/12)=5/12, so
a₄ = 5/12 + (1/8)·a₄
Bring the a₄–term to the left:
a₄·(1 – 1/8) = 5/12
(7/8)·a₄ = 5/12
a₄ = (5/12)·(8/7) = 40/84 = 10/21.

Hence starting from state 4 the probability of eventual absorption in {0,3} is 10/21.

CSIR NET Mathematical Science Mock Test - 2 - Question 15

Let f be an entire function. Which of the following statement is FALSE?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 15

Concept:
By Liouville's theorem, any entire function (a function that is holomorphic across the entire complex plane) that is bounded must be constant.

Explanation:
Option 1:

If both the real and imaginary parts of f are bounded, the entire function f itself is bounded.
By Liouville’s theorem, f must be constant.
This statement is true.

Option 2:

If is bounded, then f is constant.

The exponential function grows very fast. If the exponential of the sum of the absolute values of the real and imaginary parts is bounded, then both real and imaginary parts of f must be very restricted (in fact, constant). Therefore, f must be constant.
This statement is true.

Option 3:
If the sum and the product are bounded, then f is constant.
Boundedness of both the sum and product of and imposes significant restrictions on the behavior of f. If both these quantities are bounded, then f must be constant.
This statement is true.

Option 4:
If is bounded, then f is constant.
The sine function is inherently bounded (since sin(x) ∈ [-1, 1] for any real x, so the boundedness of does not necessarily imply that f is constant. The function f could still vary without violating this condition.
This statement is false.
Hence, our answer is option 4).

CSIR NET Mathematical Science Mock Test - 2 - Question 16

Let  and consider the symmetric bilinear form on R4 given by (v, w) = vt Aw, for v, w ∈ ℝ4. Which of the following statements is true?

CSIR NET Mathematical Science Mock Test - 2 - Question 17

Let X1, X2 be a random sample from N(0, σ2) distribution, where σ > 0 and N(μ, σ2) denotes a normal distribution with mean μ and variance σ2. Suppose, for some constant c, (c(X12 + X22), ∞) is a confidence interval for variance σ2 with confidence coefficient 0.95. Then the value of c is equal to

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 17

Concept:
Chi-Squared Distribution:

The sum of squares of independent normally distributed random variables follows a chi-squared distribution. Specifically, for X1 and X2 drawn from , the expression follows a chi-squared distribution with 2 degrees of freedom, scaled by σ2 :

The chi-squared distribution is crucial for estimating the variance σ2 from a sample.

Confidence Interval for Variance:
A confidence interval for the variance σ2 is derived from the chi-squared distribution. The general form of a confidence interval for σ2 is based on the chi-squared statistic where s2 is the sample variance.

and are the critical values from the chi-squared distribution with n-1 degrees of freedom.

Explanation:

We are given

X1 and X2 are a random sample from , where denotes a normal distribution with mean μ and variance σ2 .
The confidence interval is associated with the variance σ2 and has a confidence coefficient of 0.95.
We need to find the value of c in the equation , where this expression helps define a confidence interval.
Since X1and X2 are independent and come from a normal distribution , their squares follow a chi-squared distribution with 2 degrees of freedom, scaled by σ2 . Specifically 
The sum of squares can be used to construct a confidence interval for the variance σ2.
The expression is related to the chi-squared distribution. The confidence interval is based on the quantiles of the chi-squared distribution. For a 95% confidence interval, the confidence coefficient is 0.95, which means we need the quantiles of the chi-squared distribution at 5% significance level (0.05).

The constant c can be related to the quantiles of the chi-squared distribution. Given the confidence coefficient 0.95, we expect c to be derived from the logarithmic relation tied to the chi-squared distribution and the 5% significance level.

From statistical tables, for a 95% confidence interval, we use \ln(0.05) in the expression for c .
This is derived based on the chi-squared distribution quantile function.
Based on the above understanding, the correct value of c is

Thus, the correct answer is Option 3).

CSIR NET Mathematical Science Mock Test - 2 - Question 18

​Suppose x(t) is the solution of the following initial value problem in ℝ2 ẋ = Ax, x(0) = x0, where A = .

Which of the following statements is true?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 18

Concept:
Solution of ODE x'(t) = Ax is x(t) = c1ueλ1t + c2veλ2t, where u, v are the eigenvectors corresponding to the eigenvalues λ1 and λ2 respectively and c1 and c2 are constants.

Explanation:

A =

tr(A) = 5 + 2 = 7 and det(A) = 10 - 4 = 6

Eigenvalues are given by
λ2 - tr(A)λ + det(A) = 0
λ2 - 7λ + 6 = 0
(λ - 1)(λ - 6) = 0
λ = 1, 6
Eigenvector corresponding to eigenvalue λ = 1 is given by

Eigenvector is u = 

Eigenvector corresponding to eigenvalue λ = 6 is given by

v1 - 4v2 = 0 ⇒ v1 = 4v2

Eigenvector is v = 

Hence solution is

So x(t) is not bounded solution for any x0 ≠ 0

(1) is false

does not tends to 0

So (2) is false

 does not tends to ∞ as t → ∞

(3) is false

as t → ∞, for all x0 ≠ 0.

Option (4) is correct

CSIR NET Mathematical Science Mock Test - 2 - Question 19
Let X be a Poisson random variable with mean λ. Which of the following parametric function is not estimable?
Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 19

Concept:

A parametric function f(λ) is said to be estimable if there exist g(X) such that E(g(X)) = f(λ) otherwise it is called not estimable.

Explanation:

Given X be a Poisson random variable with mean λ

So E(X) = λ and Var(X) = λ

We have to find the parametric function which is not estimable.

(2): E(X) = λ so here we are getting a function g(X) = X

So it is estimable

Option (2) is false

(3): E(X2) = [E(X)]2 + Var(X) = λ2 + λ

So E(X2 - X) = E(X2) - E(X) = λ2 + λ - λ = λ2

Here we are getting the function g(X) = X2 - X

So it is estimable

Option (3) is false

(4): E = e−λ​

Here we are getting the function g(X) =

So it is estimable

Option (4) is false

Hence option (1) is correct

CSIR NET Mathematical Science Mock Test - 2 - Question 20

Suppose X1, X2, …, Xn are independently and identically distributed N(θ, 1) random variables, for θ ∈ R. Suppose denotes the sample mean and let t0.975, n−1 denote the 0.975-quantile of a Student's− t distribution with n − 1 degrees of freedom. Which of the following statements is true for the following interval ?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 20

Given X1, X2, …, Xn are independently and identically distributed N(θ, 1)


t0.975, n−1 denote the 0.975-quantile of a Student's− t distribution with n − 1 degrees of freedom.
So here confidence interval is 0.975 which is more than 0.95.
Therefore level of the significance = 2.25%
Hence option (3) is correct

CSIR NET Mathematical Science Mock Test - 2 - Question 21

Consider the quadratic form Q(x, y, z) associated to the matrix

B =

Let

S = .

Which of the following statements is FALSE?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 21

Concept:
A quadratic form is degenerate if at least one eigenvalue is 0

Explanation:

So quadratic form is Q(x, y, z) = x2 + y2 -2z2 + 2xy
Now, Q(a, b, c) = 0
a2 + b2 -2c2 + 2ab = 0....(i)

(1): On xy-plane, z = 0 so c = 0
Therefore (i) implies
a
2 + b2 + 2ab = 0 ⇒ (a + b)2 = 0 ⇒ a + b = 0
i.e., x + y = 0, which is a line

So option (1) is TRUE
(2)
On xz-plane, y = 0 so b = 0
Therefore (i) implies
a2 - 2c2 = 0 ⇒ x2 - 2z2 = 0 which is not an equation of ellipse
So option (2) is FALSE

(3): (i) ⇒ a2 + b2 -2c2 + 2ab = 0
⇒ (a + b)2 = 2c2
⇒ a + b = ± √2c

So S is the union of two planes.

Option (3) is TRUE
(4):
B =

eigenvalues of B are -2, 2, 0
So Q is a degenerate quadratic form.

Option (4) is TRUE

CSIR NET Mathematical Science Mock Test - 2 - Question 22

Let X = (X1, X2)T follow a bivariate normal distribution with mean vector (0, 0)T and covariance matrix Σ such that

Σ =

The mean vector and covariance matrix of Y = (X1, 5 − 2X2)T are

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 22

Concept:

Mean vector of Y = is E(Y) = and covariance matrix of Y is Σ =

Explanation:

Given mean vector of X = (X1, X2)T is (0, 0)T and covariance matrix Σ such that Σ =

So

E(X1) = 0, E(X2) = 0, var(X1) = 5, var(X2) = 10........(i)

cov(X1X2) = cov(X2X1) = -3................................(ii)

Now, cov(X1X2) = -3

⇒ E(X1X2) - E(X1)E(X2) = -3

⇒ E(X1X2) - 0 = -3 (using (i))

⇒ E(X1X2) = -3 ..........(iii)

Y = (X1, 5 − 2X2)T

Let Y = (Y1, Y2)T

Then Y1 = X1 and Y2 = 5 − 2X2.......(iv)

Now, E(Y1) = E(X1) = 0 and E(Y2) = 5 - 2E(X2) = 5 - 0 =5

So mean vector of Y is = .......(v)

Also var(Y1) = var(X1) = 5

var(Y2) = var(5 - 2X2) = 0 + 4var(X2) = 4 × 10 = 40

cov(Y1Y2) = E(Y1Y2) - E(Y1)E(Y2)

= E(5X1 - 2X1X2) - 0 (using (i) and (ii))

= 5E(X1) - 2E(X1X2) = 0 + 6 = 6 (using (i) and (iii))

Also cov(Y2Y1) = 6

Therefore covariance matrix of Y is

Therefore option (4) is correct.

*Multiple options can be correct
CSIR NET Mathematical Science Mock Test - 2 - Question 23

Which of the following statements is true?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 23

Let us go through all the options one by one.

1. A harmonic function u is a twice continuously differentiable function. i.e. it satisfies Laplace’s equation:
Can also be written as ∇2u = 0
Or Δu = 0
Option 1 is correct.

2) By the strong maximum principle we get:
If D is connected and there exists a point x0 ∈ D such that:
Then ϕ is constant within D.
Option 2 is correct.

3) A wave that travels continuously in a medium in the same direction without the change in its amplitude is called a traveling wave or progressive wave.
Example:
y(x, t) = a sin (kx – ωt + ϕ)
y(x, t) is the displacement of the element at a point x and t from the y-axis.
∴ Option 3 is correct.

4) If ϕ solves the initial value wave equation in one dimension, then the sum of kinetic energy and potential energy is independent of time.
∴ Option 4 is incorrect.

*Multiple options can be correct
CSIR NET Mathematical Science Mock Test - 2 - Question 24

Suppose that {an} is a non- negative sequence satisfying then the series

is

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 24

Let Sn = then

So converges for k > 1 and diverges for 0 < k ≤ 1

(1), (3), (4) correct

*Multiple options can be correct
CSIR NET Mathematical Science Mock Test - 2 - Question 25

Consider a solid torus of constant density p, formed by revolving the disc (y - b)2 + z2 ≤ a2, x = 0 about the z-axis, where 0 < a < b. Then the moment of inertia of the solid torus about the z-axis is

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 25

Concept:

Disc equation: The equation (y − b)2 + z2 ≤ a2 describes a disc centered at (0, b, 0) with radius a.

Revolution: Revolving this disc around the z -axis forms a torus. The distance r from the z - axis to a mass element on the torus is y, but y = b + r, where r' is a point within the disc radius.

Explanation:

, where r is the perpendicular distance from the z -axis, dm = ρdV is the mass element and ρ is the constant density. For this particular geometry, we are revolving the disc described by the equation  around the z - axis, where .

After solving this integral, the correct formula for the moment of inertia of the solid torus about the z -axis is

Hence option 2) is correct.

*Multiple options can be correct
CSIR NET Mathematical Science Mock Test - 2 - Question 26

Let X denote the topological space R with the cofinite topology (i.e., the finite complement topology) and let Y denote the topological space R with the Euclidean topology. Which of the following statements are true?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 26

Concept:
1. X is the real numbers R with the cofinite topology (also called the finite complement topology).
This means that a subset A of R is closed if its complement is finite or if A = R.
2. Y is the real numbers R with the standard Euclidean topology.

Explanation:
Option 1:
In the cofinite topology, a subset is closed if its complement is finite. Since X = R has a cofinite topology, the space X is compact in this topology.
The product X × [0,1] is closed in the product topology if both X and [0, 1] are closed in their respective topologies. [0, 1] is closed in the Euclidean topology, and X is closed in the cofinite topology.
Hence, Statement 1) is true.

Option 2: X is compact in the cofinite topology (since every open cover must have a finite subcover because any open set must have a finite complement). [0, 1] is compact in the Euclidean topology (by the Heine-Borel theorem).

The product of two compact spaces in the product topology is also compact (Tychonoff's theorem).

Hence, Statement 2 is true.

Option 3: In the cofinite topology on , a space is compact if every open cover has a finite subcover. Since the cofinite topology ensures that every cover must have at least one large set with a finite complement, X is compact.

Hence, Statement 3 is true.

Option 4: X × Y is compact with respect to the product topology.

X is compact in the cofinite topology, but  with the Euclidean topology is not compact (since  is not bounded or closed in the Euclidean topology).
The product of a compact space with a non-compact space is not compact.
Hence, Statement 4 is false.

Hence, correct options 1), 2) and 3).

*Multiple options can be correct
CSIR NET Mathematical Science Mock Test - 2 - Question 27

Let X1....., Xn(n ≥ 2) be a random sample from a U(-θ, 2θ) distribution, where θ > 0 is an unknown parameter. Let X̅ = and X(n) = max {X1....., Xn}. Which of the following statements are true?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 27

Concept:

1. Maximum Likelihood Estimator (MLE):
In the uniform distribution U(−θ, 2θ), the MLE is based on the range of the data.
The MLE is influenced by the largest value in the sample because the range of the distribution is from −θ to 2θ. MLE for θ:

, where X(n) is the maximum value in the sample.

2. Method of Moments Estimator (MME):
The method of moments involves matching the sample mean to the theoretical mean of the distribution.

For U(−θ, 2θ), the theoretical mean is θ/2.

Setting the sample mean equal to the theoretical mean, we solve for θ.

MME for θ:

, where is the sample mean.

Explanation:

is the sample mean.

X(1) is the minimum of the sample (smallest observation).

X(n) is the maximum of the sample (largest observation).

For the uniform distribution U(−θ, 2θ), the likelihood function is based on the fact that the observed values must lie within the interval (−θ, 2θ). Therefore, the maximum likelihood estimator for θ will be influenced by the largest observed value in the sample, X(n). The MLE for θ is typically the largest observed value X(n) divided by 2, because the maximum value in the sample should not exceed 2θ.

Hence, the MLE for θ is
Now, let's evaluate the options related to the MLE.

Option 1: This is false because the MLE is based on the maximum observed value X(n), not the minimum.

Option 2: his statement is somewhat unconventional but logically true. Since X(n) is the smallest value, the estimator should still involve the largest value X(n). So, the MLE is indeed  and taking the maximum with -X(1) could ensure that the parameter is positive.

True.

The method of moments involves equating the sample moments to the theoretical moments of the distribution.

The mean of the distribution is:


Equating this to the sample mean , we get,


Solving for θ, we get the method of moments estimator

Option 3: This is true based on the calculation above.

Option 4: This is false. The correct MME is , not .

Hence, correct options are 2) and 3).

*Multiple options can be correct
CSIR NET Mathematical Science Mock Test - 2 - Question 28

Let f : [0, 1] → [1, ∞) be defined by , For n ≥ 1, let pn(x) = 1 + x + ....+ xn, Then which of the following statements are true?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 28

Concept:

Pointwise Convergence:

Let {fn(x)} be a sequence of functions defined on a domain D. The sequence {fn(x)} is said to converge pointwise to a function f(x) on D if, for every point x ∈ D and for every ϵ > 0, there exists an integer N such that for all n ≥ N, the following condition holds |fn(x) − f(x)| < ϵ.
In other words, for each fixed point x ∈ D, the values of the functions fn(x) get arbitrarily close to f(x) as n → ∞.

Uniform Convergence:
Let {fn(x)} be a sequence of functions defined on a domain D. The sequence {fn(x)} is said to converge uniformly to a function f(x) on D if for every ϵ > 0, there exists an integer N such that for all n ≥ N and for all x ∈ D, the following condition holds |fn(x) − f(x)| < ϵ.

Explanation:


For n≥1 , let pn(x) = 1 + x + x+ ⋯ + xn. This is the sum of the first n + 1 terms of a geometric series.

We know that the infinite geometric series , which means pn(x) is an approximation of f(x) as n → ∞.

Option 1: The function blows up as x → 1, meaning that as we get closer to 1, the function value grows without bound. This implies that f(x) is not uniformly continuous because the difference in function values for close inputs near 1 can be arbitrarily large.
Option 1) is true.

Option 2: The sequence pn(x) = 1 + x + ⋯ + xn is a partial sum of the geometric series, and we know that the infinite sum converges to . Therefore, pn(x) converges to f(x) pointwise on [0, 1).
Option 2 is true.

Option 3: Uniform convergence requires that the convergence happens uniformly across the entire interval.

Near x = 1 , the function f(x) grows very large, and the sequence pn(x) does not converge uniformly because the convergence slows down significantly near x = 1.
Option 3 is false.

Option 4: This is true because for any c < 1 , the function is continuous and well-behaved on the interval [0, c], and the sequence pn(x) will converge uniformly on compact subintervals away from 1.
Option 4 is true.
The correct options are Option 1), Option 2), and Option 4).

*Multiple options can be correct
CSIR NET Mathematical Science Mock Test - 2 - Question 29

Let τ be the smallest topology on the set ℝ containing β = {[a, b)|a < b ; a, b ∈ R}

Which of the following statements are true?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 29

Concept:
A topological space (X, τ) is called a Hausdorff space if for any two distinct points x , y ∈ X, there exist disjoint open sets U and V such that x ∈ U , y ∈ V  and U ∩ V = ∅

Explanation:
Option 1.
β is a basis for topology τ is true: The collection β consists of open intervals of the form [a, b) for a < b. 
The smallest topology containing these sets is generated by taking unions of sets from β and includes the empty set and ℝ itself. Thus, β serves as a basis for τ .

Option 2. ℝ is compact in the topology τ is false : In general, ℝ is not compact in the standard topology (or any topology generated by open intervals) because it is not closed and bounded. The Heine-Borel theorem states that a subset of ℝ is compact if and only if it is closed and bounded, which ℝ is not.

Option 3. Topology τ is the same as the Euclidean topology is false: While both topologies are generated by open intervals, the smallest topology containing β might include sets that are not open in the standard Euclidean topology.
Thus, τ may not include all open sets of the Euclidean topology.

Option 4. Topology τ is Hausdorff is true: A topology is Hausdorff if for any two distinct points x , y ∈ ℝ, there exist disjoint open sets containing each point. Since τ is generated by open intervals, it is possible to find such intervals for any two distinct points in ℝ , confirming that τ is Hausdorff.
The true statements are Option 1) and 4).

*Multiple options can be correct
CSIR NET Mathematical Science Mock Test - 2 - Question 30

Let Y1....Yn (n ≥ 2) be independent observations; Yi ∼ N(βxi, σ2), i = 1,...,n; where x1,...,xn and σ2(> 0) are known constants and β ∈ ℝ is an unknown parameter. Consider N(β0, τ2) prior for the parameter β, where β0 and τ2(> 0) are known constants, and N(μ, λ2) denotes a normal distribution with mean μ and variance λ2, Suppose ; are observed sample means. Under squared error loss function, which of the following statements are true?

Detailed Solution for CSIR NET Mathematical Science Mock Test - 2 - Question 30

Concept: Bayesian estimation problem where we are provided with observations Y1,…,Yn, each following a normal distribution with mean βxi and variance σ2. The parameter β has a prior distribution N(β0, T2),

Explanation:
Option 1:
This is true. When the prior variance T→ 0, the prior becomes highly concentrated around β0 .
Therefore, the Bayes estimate will heavily rely on the prior and converge to β0.

Option 2: This is false. As T→ 0 , the Bayes estimate will tend to β0 , not the ratio of the sample means y/x .

Option 3: This is true. When T→ ∞, the prior becomes non-informative, and the Bayes estimate relies more on the likelihood, which corresponds to the BLUE.

Option 4: This is also true. As T→ ∞ , the prior has less influence, and the estimate approaches the MLE of β, which is based on the likelihood alone.

Correct options: 1), 3), 4).

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