Playing With Numbers

Short Answer Questions(SAQs)

What are prime numbers?

Prime numbers are numbers that have only 2 factors – 1 and the number itself.

What is a divisibility test?

A divisibility test is an easy way of finding out whether a given integer is divisible by a fixed divisor without executing the division, usually by examining its digits.

What are ‘common factors’?

A common factor is a number that can be divided into two different numbers, without leaving a remainder.

MCQs

1. Which of the following is a prime number?

(a) 4

(b) 6

(c) 7

(d) 9

► (c) 7 is a prime number because it has only two factors: 1 and itself.

2. Which of these is not a common factor of 12 and 16?

(a) 2

(b) 3

(c) 4

(d) 1

► (b) 3 is not a common factor of 12 and 16 since 16 is not divisible by 3.

3. What is the smallest prime number?

(a) 0

(b) 1

(c) 2

(d) 3

► (c) 2 is the smallest and the only even prime number.

4. Which number is divisible by 5?

(a) 21

(b) 30

(c) 44

(d) 18

► (b) 30 is divisible by 5 because it ends in 0.

5. What is the LCM of 4 and 5?

(a) 9

(b) 10

(c) 20

(d) 25

► (c) 20 is the least common multiple of 4 and 5.

6. Which number is divisible by both 2 and 3?

(a) 9

(b) 18

(c) 25

(d) 13

► (b) 18 is divisible by both 2 and 3.

7. A number divisible by 10 must end in:

(a) 0

(b) 5

(c) 2

(d) 9

► (a) 0

8. HCF of 12 and 18 is:

(a) 2

(b) 3

(c) 6

(d) 12

► (c) 6 is the greatest common factor of 12 and 18.

9. What is a factor of every number?

(a) 0

(b) 1

(c) 2

(d) 3

► (b) 1 is a factor of every number.

10. Which number is not divisible by 2?

(a) 14

(b) 17

(c) 20

(d) 6

► (b) 17 is not divisible by 2 since it is odd.

11. Which number is a multiple of both 3 and 4?

(a) 6

(b) 12

(c) 9

(d) 18

► (b) 12 is a multiple of both 3 and 4.

12. The sum of any two odd numbers is:

(a) Odd

(b) Even

(c) Prime

(d) Multiple of 3

► (b) Even

13. Which of these is not a prime number?

(a) 2

(b) 3

(c) 9

(d) 7

► (c) 9 is not a prime number because it has more than two factors.

14. What is the HCF of 8 and 15?

(a) 1

(b) 2

(c) 4

(d) 5

► (a) 1

15. A number divisible by 9 must have digits that:

(a) End in 9

(b) Are all even

(c) Add up to 9 or a multiple of 9

(d) Are all the same

► (c) The sum of its digits must be a multiple of 9.

16. LCM of 3, 4 and 6 is:

(a) 12

(b) 24

(c) 18

(d) 6

► (a) 12 is the least common multiple of 3, 4 and 6.

17. A number divisible by 6 must be divisible by:

(a) 2 and 3

(b) 3 and 4

(c) 2 and 4

(d) 2 and 5

► (a) A number divisible by 6 must be divisible by both 2 and 3.

18. What is the LCM of 10 and 15?

(a) 5

(b) 30

(c) 45

(d) 15

► (b) 30 is the smallest number divisible by both 10 and 15.