-9.01% is the change from 999 to 909
Calculation steps:
[( 909 - 999 ) ÷ 999] x 100 = -9.01%
Formula
Percentage change = [(909 - 999) / 999] x 100
Subtract the new number by the original number
909 - 999 = -90
-90 ÷ 999 = -0.09009009009009009
-0.09009009009009009 x 100 = -9.01%