-21.88% is the change from 320 to 250
Calculation steps:
[( 250 - 320 ) ÷ 320] x 100 = -21.88%
Formula
Percentage change = [(250 - 320) / 320] x 100
Subtract the new number by the original number
250 - 320 = -70
-70 ÷ 320 = -0.21875
-0.21875 x 100 = -21.88%