-82.12% is the change from 509 to 91
Calculation steps:
[( 91 - 509 ) ÷ 509] x 100 = -82.12%
Formula
Percentage change = [(91 - 509) / 509] x 100
Subtract the new number by the original number
91 - 509 = -418
-418 ÷ 509 = -0.8212180746561886
-0.8212180746561886 x 100 = -82.12%