900% is the change from 40 to 400
Calculation steps:
[( 400 - 40 ) ÷ 40] x 100 = 900%
Formula
Percentage change = [(400 - 40) / 40] x 100
Subtract the new number by the original number
400 - 40 = 360
360 ÷ 40 = 9
9 x 100 = 900%
Example