-38.9% is the change from 820 to 501
Calculation steps:
[( 501 - 820 ) ÷ 820] x 100 = -38.9%
Formula
Percentage change = [(501 - 820) / 820] x 100
Subtract the new number by the original number
501 - 820 = -319
-319 ÷ 820 = -0.38902439024390245
-0.38902439024390245 x 100 = -38.9%