Cambridge International Mathematics

18 Assumed Knowledge (Number)

Example 25 Self Tutor

In one year, Maria’s height increases from 150 cm in the ratio31 : 30.

Find Maria’s new height.

The second number in the ratio represents the original quantity. The

first number represents the final quantity.

Maria’s original height=30parts= 150cm

) 1 part=5cm

) Maria’s new height=31parts

=31£ 5 cm

= 155cm

Example 26 Self Tutor

On a particular day, 1 Australian dollar is worth 0 : 94 US dollars.

How many Australian dollars can be exchanged for$20US?

Suppose$20US is worthxAustralian dollars.

) 1:0:94 =x:20

) 100 : 94 =x:20

If 94 parts=20

then 1 part=^2094

) 100 parts=^2094 £ 100 ¼ 21 : 28

) $20US can be exchanged for$21: 28 AUD.

Use theunitary methodto solve these problems:

1 The ratio of Bob’s weight to Colin’s weight is6:7. If Bob

weighs 83 : 7 kg, how much does Colin weigh?

2 If Kayo and Sally split their profits in the ratio of5:4

respectively and Kayo gets$23 672, how much does Sally

get, to the nearest dollar?

3 Jack’s lawn is on average 8 : 3 cm high. The ratio of height

of Jack’s lawn to Henri’s lawn is1:1: 13. Find the average

height of Henri’s lawn.

4 The ratio of water to alcohol in a bottle of wine is15 : 2. If there are 662 ml of water in the bottle,

what is the quantity of alcohol in the bottle?

5 On a particular day, one British pound is worth 1 : 26 euros. How many pounds can be exchanged for

50 euros?

EXERCISE F.4

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