-55% is the change from 20 to 9
Calculation steps:
[( 9 - 20 ) ÷ 20] x 100 = -55%
Formula
Percentage change = [(9 - 20) / 20] x 100
Subtract the new number by the original number
9 - 20 = -11
-11 ÷ 20 = -0.55
-0.55 x 100 = -55%
Example