50% is the change from 640 to 960
Calculation steps:
[( 960 - 640 ) ÷ 640] x 100 = 50%
Formula
Percentage change = [(960 - 640) / 640] x 100
Subtract the new number by the original number
960 - 640 = 320
320 ÷ 640 = 0.5
0.5 x 100 = 50%
Example