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Ratio, proportion and percentages

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1.2.1 Try some yourself

Activity 1

A friend is painting the inside walls of a garage. So far she has used a 2 litre tin of emulsion paint and covered an area of 9 m2. She needs some more paint. How much more would you advise her to purchase if she intends to paint all the walls and ceiling, which is a total area of 75 m2.

An area of 9 m2 requires 2 litres of paint. The ratio of paint to area is 2 to 9 or . So an area of 1 m2 would require of a litre of paint. She needs to paint an area of (75 − 9) m2 or 66 m2. This will require    litres of paint (i.e. 14.666 67) litres or approximately 15 litres to the nearest litres. So she needs 15 more litres of paint (rounded up).

Activity 2

If the ratio of distance measured in miles to the same distance measured in kilometres is five to eight, which is the higher speed limit, 70 miles per hour or 110 kilometres per hour?