Question

A number first increases by 20% and then decreases by 20%. Find the percentage increase or decrease on the whole.

Answer 1

Let the number be 100

In 1st condition,

increase = 20% of 100

`= 20/100 xx 100 = 20`

∴ Number after this increase = 100 + 20 = 120

In 2nd condition,

Decrease = 20 % of 120

`= 20/100 xx120 = 24`

∴ Number after this decrease = 120 - 24 = 96

⇒ Total decrease on the whole = 24 - 20 = 4

and the percentage decrease on the whole

`= 4/100 xx 100 = 4%`