-12.9% is the change from 310 to 270
Calculation steps:
[( 270 - 310 ) ÷ 310] x 100 = -12.9%
Formula
Percentage change = [(270 - 310) / 310] x 100
Subtract the new number by the original number
270 - 310 = -40
-40 ÷ 310 = -0.12903225806451613
-0.12903225806451613 x 100 = -12.9%