Question

Last month the cost of using the air pump at a garage was 20p.

This month the cost of using the air pump is 50p.

Tom says,

"50 = 20 = 2. 5 so the cost of using the air pump has increased by 250%"

(a) Is Tom correct?

Explain your answer.

Answer 1

Tom is incorrect

The cost of using the air pump has increased by 150%

Explanation:

Tom is incorrect

percent change = [ (difference between initial and final value) ÷ initial value] × 100

⇒ [ (50 - 20) ÷ 20) × 100 = 150%

Therefore, the cost of using the air pump has increased by 150%