3090% is the change from 20 to 638
Calculation steps:
[( 638 - 20 ) ÷ 20] x 100 = 3090%
Formula
Percentage change = [(638 - 20) / 20] x 100
Subtract the new number by the original number
638 - 20 = 618
618 ÷ 20 = 30.9
30.9 x 100 = 3090%
Example