Mental Maths Questions and Answers: Linear Equations in One Variable | Mental Mathematics for Class 8 PDF Download

Q1: Find the value of x: 3x + 4 = 6(x - 1) + 7
Ans: 1

Q2: Find the value of
Ans: 0

Q3: Find the value of
Ans: 2

Q4: Find the value of
Ans: 7

Q5: Find the value of
Ans: 1/5

Q6: Find the value of c: 2(c - 3) = 5(2c + 2)
Ans: -2

Q7: Solve: 0.16(5* + 1) = 0.4x + 0.16
Ans: 0

Q8: Solve for x: x² - (x + 1)(x - 2) = 0
Ans: -2

Q9: What is the number which when added to 15 times of itself gives 208.
Ans: 13

Q10: A number is as much greater than 84 as it is less than 108. What is the number?
Ans: 96

Q11: The sum of three consecutive natural numbers is 33. Find the numbers.
Ans: 10,11,12

Q12: Two consecutive sides of a rectangle are in the ratio 3:2. If its perimeter is 150cm, then find its area?
Ans: 1350 sq.cm

Q13: A number consists of two digits whose sum is 9. If 27 is added to the number its digits are reversed. Find the number.
Ans: 36

Q14: A man sold an umbrella for ₹495 and gained 10% on it. Find its cost price.
Ans: ₹450

Q15: 3/4 th of a number is 20 more than half of the same number. What is the 4 number?
Ans: 80

Q16: Three fourth of a number exceeds its one third by 60. What is the number?
Ans: 144

Q17: Sum of three consecutive multiples of 4 is 108. Find the numbers.
Ans: 32, 36, 40

Q18: A box of toffees is divided among 24 children. They will get 5 toffees each. How many would each get, if the number of children is reduced by 4?
Ans: 6

Q19: Four fifth of a certain number is 64. What will be half of that number?
Ans: 40

Q20: Sides of a triangle are in the ratio 2:3:4. If its perimeter is 225m, find the length of smallest side.
Ans: 50 m

Q21: Find the number whose fifth part increased by 5 is equal to its fourth part decreased by 5.
Ans: 200

Q22: Find three consecutive odd natural numbers whose sum is 147.
Ans: 47, 49, 51

Q23: Find three consecutive even natural numbers whose sum is 234.
Ans: 76, 78, 80

Q24: The sum of two numbers is 95. If one number exceeds the other by 15, find the smaller number.
Ans: 40

Q25: The sum of three consecutive natural numbers is 108. Find the middle number.
Ans: 36

Q26: The base of an isosceles triangle is 8 cm and its perimeter is 20 cm. Find the length of equal sides.
Ans: 6 cm

Q27: Four fifth of a number is greater than three fourth of the same number by 4. Find the number.
Ans: 80

Q28: The width of a rectangle is two third of its length. If the perimeter is 180m, find its dimensions.
Ans: 54 m,  36 m

Q29: If 10 is added to four times a certain number, the result is 5 less than five times the number. Find the number.
Ans: 15

Q30: The average age of 3 girls is 20 years and their ages are in the ratio 3:5.7. Find the age of the eldest girl.
Ans: 28 years

Q31: The perimeter of a rectangle is numerically equal to the area of the rectangle. If the width of the rectangle is 3cm, find its length.
Ans: 6 cm

Q32: An angle is double of its supplementary angle. Find the complementary angle of its supplementary angle.
Ans: 30º

Q33: The number of boys and girls in a class are in the ratio 4:7. If the number of boys are 6 less than the number of girls. Find the number of students in the class.
Ans: 22

Q34: After 4 years 'A' will be 3 times as old as he was 4 years ago. Find his present age.
Ans: 8 years

Q35: In an examination a student scores 4 marks for every correct answer and loses 1 mark for every wrong answer. If he attempts 75 questions and scores 125 marks, then find the number of correct questions he answered.
Ans: 40

Q36: 'A' is 20 years older than B, he is also 6 times as old as B. What are their ages?
Ans: A’s age = 24 years
B’s age = 4 years

Q37: One third of a number is 10 less than two third of the number. Find the number.
Ans: 30

Q38: One of the angles of a triangle is equal to the sum of the other two angles. If the ratio of the other two angles is 2:3, find the angles of the triangles.
Ans: 30º,54º,90º

Q39: Find three consecutive even natural numbers whose sum is 216.
Ans: 70,72,74

Q40: Find a number whose double is 45 greater than its half.
Ans: 30

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