Page 115 - MAT KS3 Y8 Cambridge CheckPoint

11.2 Percentage increases and decreases

11.2 Percentage increases and decreases

Percentages are often used to describe increases or decreases.
Examples: The population of the town decreased by 13%.
I received a 7% pay rise. A decrease is often called a
The price was reduced by 30%. reduction.
Production rose by 150%.

You can find the result of an increase or decrease in two steps.
c First, calculate the increase or decrease.
d Then add it to or subtract it from the original amount.

Worked example 11.2

Yi-ling bought a car for $15 800. After a year it was worth 20% less. How much was it worth
after a year?

20% = 1 You could also say 20% = 0.2 and multiply by that decimal.
5
1 of 15 800 = 15 800 ÷ 5 = 3160 This is the reduction in value.
5
15 800 − 3160 = 12 640 Subtract 20% from the original cost.
The car is worth $12 640.

✦ Exercise 11.2

1 a Find 15% of $60. b Increase $60 by 15%. c Decrease $60 by 15%.

2 a Find 70% of 3200 people. b Increase 3200 by 70%. c Decrease 3200 by 70%.
3 a Find 2% of 19.00. b Increase 19.00 by 2%. c Decrease 19.00 by 2%.
4 Read what Tanesha says. How much will she have if she increases her savings by:
a 10% b 50% c 70%
d 100% e 120%?
I have saved $240.

5 The population of a town is 45 000.
The population is expected to rise by 15% in the next ten years.
Estimate the population in ten years’ time.

6 A metal bar is 1.800 metres long.
It is heated and the length increases by 0.5%.
How long is the bar now?
Item Price in $ US
7 A shop lists its prices in a table. Table 280
a In a sale, all the prices are reduced by 30%.
Calculate the sale prices. Armchair 520
b How much would you save if you bought all four Bed 190
items in the sale? Mattress 430
11 Percentages 113