31900% is the change from 2 to 640
Calculation steps:
[( 640 - 2 ) ÷ 2] x 100 = 31900%
Formula
Percentage change = [(640 - 2) / 2] x 100
Subtract the new number by the original number
640 - 2 = 638
638 ÷ 2 = 319
319 x 100 = 31900%
Example