3900% is the change from 20 to 800
Calculation steps:
[( 800 - 20 ) ÷ 20] x 100 = 3900%
Formula
Percentage change = [(800 - 20) / 20] x 100
Subtract the new number by the original number
800 - 20 = 780
780 ÷ 20 = 39
39 x 100 = 3900%
Example