-80% is the change from 40 to 8
Calculation steps:
[( 8 - 40 ) ÷ 40] x 100 = -80%
Formula
Percentage change = [(8 - 40) / 40] x 100
Subtract the new number by the original number
8 - 40 = -32
-32 ÷ 40 = -0.8
-0.8 x 100 = -80%
Example