-87.1% is the change from 310 to 40
Calculation steps:
[( 40 - 310 ) ÷ 310] x 100 = -87.1%
Formula
Percentage change = [(40 - 310) / 310] x 100
Subtract the new number by the original number
40 - 310 = -270
-270 ÷ 310 = -0.8709677419354839
-0.8709677419354839 x 100 = -87.1%