Chapter 3: Playing With Numbers

Exercise 3.1

Q1. 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

Answer.

(a) 24 = 1 x 24 = 2 x 12 = 3 x 8 = 4 x 6 = 6 x 4

Factors of 24 = 1, 2, 3, 4, 6, 12, 24.

(b) 15 = 1 x 15 = 3 x 5 = 5 x 3

Factors of 15 = 1, 3, 5, 15.

(c) 21 = 1 x 21 = 3 x 7 = 7 x 3

Factors of 21 = 1, 3, 7, 21.

(d) 27 = 1 x 27 = 3 x 9 = 9 x 3

Factors of 27 = 1, 3, 9, 27.

(e) 12 = 1 x 12 = 2 x 6 = 3 x 4 = 4 x 3

Factors of 12 = 1, 2, 3, 4, 6, 12.

(f) 20 = 1 x 20 = 2 x 10 = 4 x 5 = 5 x 4

Factors of 20 = 1, 2, 4, 5, 10, 20.

(g) 18 = 1 x 18 = 2 x 9 = 3 x 6

Factors of 18 = 1, 2, 3, 6, 9, 18.

(h) 23 = 1 x 23

Factors of 23 = 1, 23.

(i) 36 = 1 x 36 = 2 x 18 = 3 x 12 = 4 x 9 = 6 x 6

Factors of 36 = 1, 2, 3, 4, 6, 9, 12, 18, 36.

Q2. Write first five multiples of:

(a) 5

(b) 8

(c) 9

Answer.

To  find multiples of a number, recall its number table.

(a) 5 x 1 = 5, 5 x 2 = 10, 5 x 3 = 15, 5 x 4 = 20, 5 x 5 = 25

First five multiples of 5 are 5, 10, 15, 20, 25.

(b) 8 x 1 = 8, 8 x 2 = 16, 8 x 3 = 24, 8 x 4 = 32, 8 x 5 = 40

First five multiples of 8 are 8, 16, 24, 32, 40.

(c) 9 x 1 = 9, 9 x 2 = 18, 9 x 3 = ,27, 9 x 4 = 36, 9 x 5 = 45

First five multiples of 9 are 9, 18, 27, 36, 45.

Q3. Match the items in column 1 with the items in column 2:

Column 1	Column 2
(i) 35	(a) Multiple of 8
(ii) 15	(b) Multiple of 7
(iii) 16	(c) Multiple of 70
(iv) 20	(d) Factor of 30
(v) 20	(e) Factor of 50

Answer.

(i) → (b)

(ii) → (d)

(iii) → (a)

(iv) → (f)

(v) → (e)

Q4. Find all the multiples of 9 up to 100.

Answer. Multiples of 9 up to 100 are:

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