-90% is the change from 100 to 10
Calculation steps:
[( 10 - 100 ) ÷ 100] x 100 = -90%
Formula
Percentage change = [(10 - 100) / 100] x 100
Subtract the new number by the original number
10 - 100 = -90
-90 ÷ 100 = -0.9
-0.9 x 100 = -90%
Example