-49.06% is the change from 640 to 326
Calculation steps:
[( 326 - 640 ) ÷ 640] x 100 = -49.06%
Formula
Percentage change = [(326 - 640) / 640] x 100
Subtract the new number by the original number
326 - 640 = -314
-314 ÷ 640 = -0.490625
-0.490625 x 100 = -49.06%