-98.9% is the change from 820 to 9
Calculation steps:
[( 9 - 820 ) ÷ 820] x 100 = -98.9%
Formula
Percentage change = [(9 - 820) / 820] x 100
Subtract the new number by the original number
9 - 820 = -811
-811 ÷ 820 = -0.9890243902439024
-0.9890243902439024 x 100 = -98.9%