-82.19% is the change from 511 to 91
Calculation steps:
[( 91 - 511 ) ÷ 511] x 100 = -82.19%
Formula
Percentage change = [(91 - 511) / 511] x 100
Subtract the new number by the original number
91 - 511 = -420
-420 ÷ 511 = -0.821917808219178
-0.821917808219178 x 100 = -82.19%