-75% is the change from 320 to 80
Calculation steps:
[( 80 - 320 ) ÷ 320] x 100 = -75%
Formula
Percentage change = [(80 - 320) / 320] x 100
Subtract the new number by the original number
80 - 320 = -240
-240 ÷ 320 = -0.75
-0.75 x 100 = -75%
Example