-63.91% is the change from 640 to 231
Calculation steps:
[( 231 - 640 ) ÷ 640] x 100 = -63.91%
Formula
Percentage change = [(231 - 640) / 640] x 100
Subtract the new number by the original number
231 - 640 = -409
-409 ÷ 640 = -0.6390625
-0.6390625 x 100 = -63.91%