-21.1% is the change from 820 to 647
Calculation steps:
[( 647 - 820 ) ÷ 820] x 100 = -21.1%
Formula
Percentage change = [(647 - 820) / 820] x 100
Subtract the new number by the original number
647 - 820 = -173
-173 ÷ 820 = -0.21097560975609755
-0.21097560975609755 x 100 = -21.1%