-20% is the change from 320 to 256
Calculation steps:
[( 256 - 320 ) ÷ 320] x 100 = -20%
Formula
Percentage change = [(256 - 320) / 320] x 100
Subtract the new number by the original number
256 - 320 = -64
-64 ÷ 320 = -0.2
-0.2 x 100 = -20%
Example