-88.9% is the change from 820 to 91
Calculation steps:
[( 91 - 820 ) ÷ 820] x 100 = -88.9%
Formula
Percentage change = [(91 - 820) / 820] x 100
Subtract the new number by the original number
91 - 820 = -729
-729 ÷ 820 = -0.8890243902439025
-0.8890243902439025 x 100 = -88.9%