Question

Tonya said the percent increase from 25 to 40 is 37.5%. Describe Tonya's error and give the correct percent increase?

Answer 1

The absolute increase is `40-25=15`

Explanation:

The error is that this was taken as a percentage of the new situation:
`15/40xx100%=37.5%`

But increase (or decrease) is always taken from the old situation:
`15/25xx100%=60%`

The rule is:
Increase/decrease% `=("New"-"Old")/("Old")xx100%`

Where a negative outcome means a decrease.