Page 26 - Cambridge+Checkpoint+Mathematics+Coursebook+9

3.1 Multiplying and dividing decimals mentally

2 Work these out mentally.
a 4 ÷ 0.2 b 9 ÷ 0.3 c 25 ÷ 0.5 d 12 ÷ 0.4 e 60 ÷ 0.1
f 2 ÷ 0.05 g 6 ÷ 0.02 h 28 ÷ 0.07 i 24 ÷ 0.12 j 45 ÷ 0.15

3 Arrange these cards into groups that have the same answer.

A 3 × 0.05 B 30 × 0.05 C 0.3 × 0.05 D 0.005 × 3

E 500 × 0.03 F 5 × 0.03 G 0.3 × 5 H 0.3 × 0.5

I 0.003 × 5 J 0.005 × 30 K 0.03 × 0.5 L 0.5 × 3

4 Which answer is correct, A, B, C or D?
a 0.8 ÷ 0.02 = A 0.04 B 0.4 C 4 D 40
b 4.5 ÷ 0.5 = A 0.9 B 9 C 90 D 900
c 0.09 ÷ 0.003 = A 0.3 B 3 C 30 D 300
d 3.6 ÷ 0.006 = A 0.6 B 6 C 60 D 600
5 Work these out mentally.
a 0.6 × 0.2 b 4.5 × 0.3 c 0.18 × 0.4 d 0.06 × 2.5 e 0.11 × 0.5
f 0.6 ÷ 0.02 g 2.7 ÷ 0.3 h 0.45 ÷ 0.09 i 0.28 ÷ 0.04 j 3.6 ÷ 0.09
6 This is part of Hassan’s homework.
He has jotted down some workings to help Question 24 025
×
.
Question Work out mentally
Question
×
.
him answer the question. 02 06 .
He has made a mistake.
Explain the mistake Hassan has made and Answer Top: 1 of 24 = 6 Bottom: 1.2
4
work out the correct answer. 6 ÷ 1.2 = 60 ÷ 12 = 5
7 Work out the answers mentally. Use jottings to help.
.
03
025
.
a 48 × 05 b 120 × 15 . . c 84 × 0002 d 120 × 04 . × 01 .
08 ×
35 ×
02 . ×
004 ×
.
.
015
3
.
.
8 a Work these out mentally.
i 8 × 0.1 ii 8 × 0.2 iii 8 × 0.3 iv 8 × 0.4 v 8 × 0.5 vi 8 × 0.6
b Use your answers to part a to answer this question.
If you multiply a number by 0.7, would you expect the answer to be larger or smaller than your
answer when you multiply the same number by 0.6?
9 a Work these out mentally.
i 12 ÷ 0.1 ii 12 ÷ 0.2 iii 12 ÷ 0.3 iv 12 ÷ 0.4 v 12 ÷ 0.5 vi 12 ÷ 0.6
b Use your answers to part a to answer this question.
If you divide a number by 0.7, would you expect your answer to be larger or smaller than when
you divide the same number by 0.6?

3 Place value, ordering and rounding 25