-18.29% is the change from 820 to 670
Calculation steps:
[( 670 - 820 ) ÷ 820] x 100 = -18.29%
Formula
Percentage change = [(670 - 820) / 820] x 100
Subtract the new number by the original number
670 - 820 = -150
-150 ÷ 820 = -0.18292682926829268
-0.18292682926829268 x 100 = -18.29%