Page 115 - Cambridge Checkpoint Mathematics Coursebook 7_Slide 02

11.1 Simple percentages

11.1 Simple percentages
Useful conversions
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Per cent just means ‘out of 100’. 2 = 50%
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• 25% means ‘25 parts out of 100’. 4 1 = 25%
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1
• 25% is another way to write . 3 = 33 %
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4 1 = 10%
So a percentage is just a diff erent way of writing a fraction. 10 1
You have already learnt how to write some simple fractions as 100 = 1%
decimals in Unit 7.

Worked example 11.1

a What percentage of this shape is shaded?
b What percentage is not shaded?

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a The fraction shaded is 20 . There are 20 identical squares. 8 are shaded.
2
8
20 = 5 8 and 20 have a common factor of 4. Divide them both by 4.
40
2 = 100 = 40% shaded Look for a fraction out of 100. 5 × 20 = 100 so multiply by 20.
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b So 60% is not shaded. The whole shape is 100%. 100% − 40% = 60%

F Exercise 11.1

1 Write down the fraction shaded in each diagram. Then write each fraction as a percentage.
a b

c d

2 Write each percentage as a fraction. Write the answers as simply as possible.
a 75% b 20% c 30% d 90% e 5%
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3 If 25% = , what fraction is 12.5%?
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11 Percentages 113