-70% is the change from 640 to 192
Calculation steps:
[( 192 - 640 ) ÷ 640] x 100 = -70%
Formula
Percentage change = [(192 - 640) / 640] x 100
Subtract the new number by the original number
192 - 640 = -448
-448 ÷ 640 = -0.7
-0.7 x 100 = -70%
Example