-6.1% is the change from 820 to 770
Calculation steps:
[( 770 - 820 ) ÷ 820] x 100 = -6.1%
Formula
Percentage change = [(770 - 820) / 820] x 100
Subtract the new number by the original number
770 - 820 = -50
-50 ÷ 820 = -0.06097560975609756
-0.06097560975609756 x 100 = -6.1%