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