-80% is the change from 850 to 170
Calculation steps:
[( 170 - 850 ) ÷ 850] x 100 = -80%
Formula
Percentage change = [(170 - 850) / 850] x 100
Subtract the new number by the original number
170 - 850 = -680
-680 ÷ 850 = -0.8
-0.8 x 100 = -80%
Example