-21.56% is the change from 320 to 251
Calculation steps:
[( 251 - 320 ) ÷ 320] x 100 = -21.56%
Formula
Percentage change = [(251 - 320) / 320] x 100
Subtract the new number by the original number
251 - 320 = -69
-69 ÷ 320 = -0.215625
-0.215625 x 100 = -21.56%