**Chapter 3 Playing With Numbers Ex 3.1**

Question 1.

Write all the factors of the following numbers:

(a) 24 (b) 15 (c) 21

(d) 27 (e) 12 (f) 20

(g) 18 (h) 23 (i) 36

Solution:

(a) Factors of 24 are:

24 = 1 x 24;

24 = 2 x 12;

24 = 3 x 8;

24 = 4 x 6

Hence, all the factors of 24 are: 1, 2, 3, 4, 6, 8, 12 and 24.

(b) Factors of 15 are:

15 = 1 x 15;

15 = 3 x 5

Hence, all the factors of 15 are: 1, 3, 5 and 15.

(c) Factors of 21 are:

21 = 1 x 21;

21 = 3 x 7

Hence, all the factors of 21 are: 1, 3, 7 and 21.

(d) Factors of 27 are:

27 = 1 x 27;

27 = 3 x 9.

Hence, all the factors of 27 are: 1, 3, 9 and 27.

(e) Factors of 12 are:

12 = 1 x 12;

12 = 2 x 6;

12 = 3 x 4

Hence, all the factors of 12 are: 1, 2, 3, 4, 6 and 12.

(f) Factors of 20 are:

20 = 1 x 20;

20 = 2 x 10;

20 = 4 x 5

Hence, all the factors of 20 are: 1, 2, 4, 5, 10 and 20.

(g) Factors of 18 are:

18 = 1 x 18;

18 = 2 x 9;

18 = 3 x 6

Hence, all the factors of 18 are: 1, 2, 3, 6, 9 and 18.

(h) Factors of 23 are:

23 = 1 x 23

Hence, all the factors of prime number 23 are: 1 and 23.

(i) Factors of 36 are:

36 = 1 x 36;

36 = 2 x 18;

36 = 3 x 12;

36 = 4 x 9;

36 = 6 x 6

Hence, all the factors of 36 are: 1, 2, 3, 4, 6, 9, 12, 18 and 36.

Question 2.

Write first five multiples of:

(a) 5 (b) 8 (c) 9

Solution:

(a) First five multiples of 5 are:

5 x 1 = 5;

5 x 2 = 10;

5 x 3 = 15;

5 x 4 = 20;

5 x 5 = 25

Hence, the required multiples of 5 are: 5, 10, 15, 20 and 25.

(b) First five multiples of 8 are:

8 x 1 = 8;

8 x 2 = 16;

8 x 3 = 24;

8×4 = 32;

8 x 5 = 40

Hence, the required multiples of 8 are: 8, 16, 24, 32 and 40.

(c) First five multiples of 9 are:

9 x 1 = 9;

9 x 2 = 18;

9 x 3 = 27;

9 x 4 = 36;

9 x 5 = 45

Hence, the required multiples of 9 are: 9,18, 27, 36 and 45.

Question 3.

Match the items in column I with the items in column II.

Solution:

(i) ↔ (b) [∵ 7 x 5 = 35]

(ii) ↔ (d) [∵ 15 x 2 = 30]

(iii) ↔ (a) [∵ 8 x 2 = 16]

(iv) ↔ (f) [∵ 20 x 1 = 20]

(v) ↔ (e) [∵ 25 x 2 = 50]

Question 4.

Find all the multiples of 9 upto 100.

Solution:

9 x 1 = 9;

9 x 2 = 18;

9 x 3 = 27;

9 x 4 = 36;

9 x 5 = 45;

9 x 6 = 54;

9 x 7 = 63;

9 x 8 = 72;

9 x 9 = 81;

9 x 10 = 90;

9 x 11 = 99

Hence, all the multiples of 9 upto 100 are:

9, 18, 27, 36, 45, 54, 63, 72, 81, 90 and 99.