-91% is the change from 100 to 9
Calculation steps:
[( 9 - 100 ) ÷ 100] x 100 = -91%
Formula
Percentage change = [(9 - 100) / 100] x 100
Subtract the new number by the original number
9 - 100 = -91
-91 ÷ 100 = -0.91
-0.91 x 100 = -91%
Example