IT

CHAPTER 11: PERCENTAGES

11.3: Percentage Changes

Ø  EXPLANATION:

·         You can use percentages to describe a change in a quantity

It could be a increase or decrease.

·         A percentage change is always calculated as a percentage of the initial value.

·         The initial value is 100%. It is important to choose the correct value to be 100%

Ø  EXAMPLE:

In May, 800 people visited a museum.

In June, 900 people visited.

In July, the number was 800 again.

a)   The percentage increase  from May to June.

b)   The percentage decrease from June to July.

1.    100% = 800

The increase is 100 (from 800 to 900)

The percentage increase is (100 : 800) x 100% = 12.5%

2.    100% = 900

The decrease is 100 (from 900 to 800 again)

The percentage decrease is (100 : 900) x 100% = 11.1%

EXERCISE 

1.    Game $40

Alain increases the price by $10. Find the percentage increase.

ü  ($10 : $40) x 100% = $25

2.    Tebor weighed 84 kg. He went running every day and began to lose mass.

After 1 month his mass was 78 kg. What was the percentage decrease?

ü  84 – 78 = 6 kg

ü  (6kg : 84kg) x 100% = 7.14%

The price of a car was $20 000. In a sale, the price decreased by 4%. After the sale it increased by 4%. (The price after the sale is $20 000 again.) 

a)    What mistake has it made?

b)   What is the correct price after the sale?