-9.68% is the change from 310 to 280
Calculation steps:
[( 280 - 310 ) ÷ 310] x 100 = -9.68%
Formula
Percentage change = [(280 - 310) / 310] x 100
Subtract the new number by the original number
280 - 310 = -30
-30 ÷ 310 = -0.0967741935483871
-0.0967741935483871 x 100 = -9.68%