-90% is the change from 310 to 31
Calculation steps:
[( 31 - 310 ) ÷ 310] x 100 = -90%
Formula
Percentage change = [(31 - 310) / 310] x 100
Subtract the new number by the original number
31 - 310 = -279
-279 ÷ 310 = -0.9
-0.9 x 100 = -90%
Example