-39.02% is the change from 820 to 500
Calculation steps:
[( 500 - 820 ) ÷ 820] x 100 = -39.02%
Formula
Percentage change = [(500 - 820) / 820] x 100
Subtract the new number by the original number
500 - 820 = -320
-320 ÷ 820 = -0.3902439024390244
-0.3902439024390244 x 100 = -39.02%