-80% is the change from 830 to 166
Calculation steps:
[( 166 - 830 ) ÷ 830] x 100 = -80%
Formula
Percentage change = [(166 - 830) / 830] x 100
Subtract the new number by the original number
166 - 830 = -664
-664 ÷ 830 = -0.8
-0.8 x 100 = -80%
Example