Mental Maths for Class 8

# Mental Maths for Class 8

## 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
•       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. 52x ÷ 57 = 53

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

11. Evaluate the following.

a. 30 – 3–2

b. 5–9 × 56

12. If x = 3, y = 2, z = 1, compute xy + yz + zx.

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

Maths Worksheets for Class 9