-5% is the change from 180 to 171
Calculation steps:
[( 171 - 180 ) ÷ 180] x 100 = -5%
Formula
Percentage change = [(171 - 180) / 180] x 100
Subtract the new number by the original number
171 - 180 = -9
-9 ÷ 180 = -0.05
-0.05 x 100 = -5%
Example