-4.48% is the change from 870 to 831
Calculation steps:
[( 831 - 870 ) ÷ 870] x 100 = -4.48%
Formula
Percentage change = [(831 - 870) / 870] x 100
Subtract the new number by the original number
831 - 870 = -39
-39 ÷ 870 = -0.04482758620689655
-0.04482758620689655 x 100 = -4.48%