-10% is the change from 10 to 9
Calculation steps:
[( 9 - 10 ) ÷ 10] x 100 = -10%
Formula
Percentage change = [(9 - 10) / 10] x 100
Subtract the new number by the original number
9 - 10 = -1
-1 ÷ 10 = -0.1
-0.1 x 100 = -10%
Example