-95.31% is the change from 640 to 30
Calculation steps:
[( 30 - 640 ) ÷ 640] x 100 = -95.31%
Formula
Percentage change = [(30 - 640) / 640] x 100
Subtract the new number by the original number
30 - 640 = -610
-610 ÷ 640 = -0.953125
-0.953125 x 100 = -95.31%