-2.35% is the change from 851 to 831
Calculation steps:
[( 831 - 851 ) ÷ 851] x 100 = -2.35%
Formula
Percentage change = [(831 - 851) / 851] x 100
Subtract the new number by the original number
831 - 851 = -20
-20 ÷ 851 = -0.023501762632197415
-0.023501762632197415 x 100 = -2.35%