## 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