-96.87% is the change from 639 to 20
Calculation steps:
[( 20 - 639 ) ÷ 639] x 100 = -96.87%
Formula
Percentage change = [(20 - 639) / 639] x 100
Subtract the new number by the original number
20 - 639 = -619
-619 ÷ 639 = -0.9687010954616588
-0.9687010954616588 x 100 = -96.87%