Mental Maths for Class 8

Mental Maths for Class 8 covers all types of problems of mental maths for class 8 students. It is very helpful to sharp the brain of class 8 students.

The Mental Maths for Class 8 covers the following topics:

Rational Numbers
Powers and Exponents
Squares and Square Roots
Cubes and Cube Roots
Playing with Numbers
Algebraic Expressions and Identities
Factorisation
Linear Equations
Applications of Percentages
Compound Interest
Direct and Inverse Proportions
Understanding Quadrilaterals
Representing Solids on a Paper
Area of Polygons
Surface Area and Volume
Data Handling and Graphs
Probability

Mental Maths Questions for Class 8

1. Which positive number is its own reciprocal?

2. Which negative number is its own reciprocal?

3. Find the absolute value of -3/7.

4. Which number should be multiplied with –6/11 to get the product 1?

5. Write a rational number between -4 and -5.

6. Divide the following rational numbers: 2/5 ÷ 5/2

7. What number should be added to –1 so as to get 7/9?

8. Find the reciprocal of –5/9.

9. Solve for x. 5^2x ÷ 5⁷ = 5³

10. Find the value of m for which x^m ÷ x = 1.

11. Evaluate the following.

a. 3⁰ – 3^–2

b. 5^–9 × 5⁶

12. If x = 3, y = 2, z = 1, compute x^y + y^z + z^x.

13. Write in the standard form.

a. 7892.3

b. 248.05

14. Express the following numbers as integers.

a. 9.8 × 10³

b. 1.06 × 10⁸

15. Express the following numbers as decimals.

a. 4 × 10^–3

b. 3.6 × 10^–5

16. Find out if 200 is a perfect square or not.

17. Express 36 as the sum of 6 odd numbers.

18. Find a Pythagorean triplet whose greatest member is 17.

19. Find a Pythagorean triplet whose smallest member is 22.

20. Estimate the square root of 360.

21. Find the least number of three digits which is a perfect square.

22. Find the smallest square number, which is divisible by each of the numbers 4, 8 and 12.

23. Express the following as a sum of odd numbers.

a. 7³

b. 9³

24. Find the cube root of 0.125 × 0.000216 × 8.

25. What is the cube root of 343 × 27?

26. A number is divisible by 4 and 6. Can you say that the number is divisible by 24?

27. Write the greatest number of 3 digits which is divisible by 2 and 5.

28. If 48x07 is divisible by 9, find the value of x.

29. Add 11a2 + 2ab + 8 and 4ab + 6.

30. Subtract 2a + ab + 6b from 5a + 4ab + 10b.

31. What must be subtracted from 5a – 2b + c to get 3a – b + 4c?

32. What should be added to 6a² – 4ab + b² to get 9a² + 2ab – b²?

33. Find the value using suitable identity.

a. (98)²

b. 103 × 97

c. 110 × 101

d. 33² – 17²

34. Find the value of x if 8x = 37² – 29².

35. Factorise the following algebraic expressions.

a. ax + bx – ay – by

b. 1 + 2t – k – 2kt

36. Factorise the following.

a. ax – b + ab – x

b. x + 6y – 6 – xy

37. Factorise each of the following.

a. a² – 9

b. 49b² – 1

38. Solve the following.

a. 5y + 2 = 12

b. 2 + 2p = 20

39. My father is four times my age. If I am 11 years old, what is my father’s age?

40. In a class of 41 students, the number of girls is 7 more than boys. How many girls are there in the class?

41. Find:

a. 20% of 1250 m

b. 18% of 990 kg

42. Raj scored 75% in an exam. If his score was 180, find the maximum marks of the exam.

43. A number is increased by 20% and then decreased by 20%. Find the net increase or decrease per cent.

44. The marked price of a pair of shoes is ₹ 1500. If the rate of discount is 5%, what is the sale price?

45. An article is purchased for ₹ 20,240 including GST of 18%. Find the price of the article before GST was added.

46. The cost price of 10 oranges is equal to the selling price of 9 oranges. Find the profit per cent.

47. What sum will amount to ₹ 9,261 at 5% per annum compound interest after 3 years?

48. Find the single discount which is equivalent to two successive discounts of 40% and 20%.

49. The population of a town is increasing at the rate of 4% per annum. If two years ago, the population of the town was 70,000, find its present population.

50. A car travels 47 km with 4 litres of petrol. How much petrol will be needed to travel a distance of 235 km?

51. A car is running at 80 km/h. How long will it take to cover 540 km at the same speed?

52. If 16 men can finish a work in 12 days, how long will 12 men take to finish the same work?

53. The angles of a quadrilateral are 120°, 82°, 48° and x°. Find the value of x.

54. If each interior angle of a regular polygon is 140°, find the number of sides of the polygon.

55. Find the sum of the interior angles of a 20-sided polygon.

56. If the length of a diagonal of a square is 8 cm, find the length of the side of the square.

57. The sides of a rectangle are in the ratio 3 : 5. Find its sides if the perimeter is 160 cm.

58. In a six-faced polyhedron, there are 6 vertices. How many edges does the polyhedron have?

59. Find the area of a rhombus, the lengths of whose diagonals are 44 cm and 26 cm.

60. The area of a rectangle of length 16 cm is the same as the area of a square of side 12 cm. Find the perimeter of the rectangle.

61. Find the area of a trapezium the lengths of whose parallel sides are 16 cm and 20 cm and the distance between them is 12 cm.

62. Find the volume of wood used to make a closed box with outer dimensions 13 m × 16 m × 10 m and thickness 50 cm.

63. Find the volume of a cylinder of height 8 cm and radius 14 cm.

64. Find the surface area of a cylinder whose base radius is 14 cm and height is 28 cm.

65. The circumference of the base of a cylinder is 15 m and its height is 84 m. Find the volume of the cylinder.

66. Find the height of a cylinder whose radius is 7 cm and total surface area is 1056 cm².

67. The ratio of the curved surface area to the total surface area of a right circular cylinder is 3 : 5. Find the ratio of the height to the radius of the cylinder.

68. In which quadrant do the points A(3, -2) and B(-4, 6) lie?

69. Find the probability of getting a spade from a pack of 52 cards in a random experiment.

70. A bag contains 5 red, 10 black and 15 green balls. A ball is taken out at random. Find the probability that the ball taken out is a red ball.

Worksheets for Maths

Maths Worksheets for Class 1

Maths Worksheets for Class 2

Maths Worksheets for Class 3

Maths Worksheets for Class 4

Maths Worksheets for Class 5

Maths Worksheets for Class 6

Maths Worksheets for Class 7

Maths Worksheets for Class 8