-81.76% is the change from 170 to 31
Calculation steps:
[( 31 - 170 ) ÷ 170] x 100 = -81.76%
Formula
Percentage change = [(31 - 170) / 170] x 100
Subtract the new number by the original number
31 - 170 = -139
-139 ÷ 170 = -0.8176470588235294
-0.8176470588235294 x 100 = -81.76%