-87.03% is the change from 640 to 83
Calculation steps:
[( 83 - 640 ) ÷ 640] x 100 = -87.03%
Formula
Percentage change = [(83 - 640) / 640] x 100
Subtract the new number by the original number
83 - 640 = -557
-557 ÷ 640 = -0.8703125
-0.8703125 x 100 = -87.03%