-21.6% is the change from 824 to 646
Calculation steps:
[( 646 - 824 ) ÷ 824] x 100 = -21.6%
Formula
Percentage change = [(646 - 824) / 824] x 100
Subtract the new number by the original number
646 - 824 = -178
-178 ÷ 824 = -0.21601941747572814
-0.21601941747572814 x 100 = -21.6%