9000% is the change from 1 to 91
Calculation steps:
[( 91 - 1 ) ÷ 1] x 100 = 9000%
Formula
Percentage change = [(91 - 1) / 1] x 100
Subtract the new number by the original number
91 - 1 = 90
90 ÷ 1 = 90
90 x 100 = 9000%
Example