-20% is the change from 80 to 64
Calculation steps:
[( 64 - 80 ) ÷ 80] x 100 = -20%
Formula
Percentage change = [(64 - 80) / 80] x 100
Subtract the new number by the original number
64 - 80 = -16
-16 ÷ 80 = -0.2
-0.2 x 100 = -20%
Example