-90% is the change from 90 to 9
Calculation steps:
[( 9 - 90 ) ÷ 90] x 100 = -90%
Formula
Percentage change = [(9 - 90) / 90] x 100
Subtract the new number by the original number
9 - 90 = -81
-81 ÷ 90 = -0.9
-0.9 x 100 = -90%
Example