-27.81% is the change from 320 to 231
Calculation steps:
[( 231 - 320 ) ÷ 320] x 100 = -27.81%
Formula
Percentage change = [(231 - 320) / 320] x 100
Subtract the new number by the original number
231 - 320 = -89
-89 ÷ 320 = -0.278125
-0.278125 x 100 = -27.81%