-22.5% is the change from 40 to 31
Calculation steps:
[( 31 - 40 ) ÷ 40] x 100 = -22.5%
Formula
Percentage change = [(31 - 40) / 40] x 100
Subtract the new number by the original number
31 - 40 = -9
-9 ÷ 40 = -0.225
-0.225 x 100 = -22.5%
Example