-19.51% is the change from 820 to 660
Calculation steps:
[( 660 - 820 ) ÷ 820] x 100 = -19.51%
Formula
Percentage change = [(660 - 820) / 820] x 100
Subtract the new number by the original number
660 - 820 = -160
-160 ÷ 820 = -0.1951219512195122
-0.1951219512195122 x 100 = -19.51%