-2.82% is the change from 638 to 620
Calculation steps:
[( 620 - 638 ) ÷ 638] x 100 = -2.82%
Formula
Percentage change = [(620 - 638) / 638] x 100
Subtract the new number by the original number
620 - 638 = -18
-18 ÷ 638 = -0.02821316614420063
-0.02821316614420063 x 100 = -2.82%