-21.32% is the change from 638 to 502
Calculation steps:
[( 502 - 638 ) ÷ 638] x 100 = -21.32%
Formula
Percentage change = [(502 - 638) / 638] x 100
Subtract the new number by the original number
502 - 638 = -136
-136 ÷ 638 = -0.21316614420062696
-0.21316614420062696 x 100 = -21.32%