-50.63% is the change from 640 to 316
Calculation steps:
[( 316 - 640 ) ÷ 640] x 100 = -50.63%
Formula
Percentage change = [(316 - 640) / 640] x 100
Subtract the new number by the original number
316 - 640 = -324
-324 ÷ 640 = -0.50625
-0.50625 x 100 = -50.63%