-1.41% is the change from 640 to 631
Calculation steps:
[( 631 - 640 ) ÷ 640] x 100 = -1.41%
Formula
Percentage change = [(631 - 640) / 640] x 100
Subtract the new number by the original number
631 - 640 = -9
-9 ÷ 640 = -0.0140625
-0.0140625 x 100 = -1.41%