-7.81% is the change from 640 to 590
Calculation steps:
[( 590 - 640 ) ÷ 640] x 100 = -7.81%
Formula
Percentage change = [(590 - 640) / 640] x 100
Subtract the new number by the original number
590 - 640 = -50
-50 ÷ 640 = -0.078125
-0.078125 x 100 = -7.81%