51.56% is the change from 640 to 970
Calculation steps:
[( 970 - 640 ) ÷ 640] x 100 = 51.56%
Formula
Percentage change = [(970 - 640) / 640] x 100
Subtract the new number by the original number
970 - 640 = 330
330 ÷ 640 = 0.515625
0.515625 x 100 = 51.56%