-50% is the change from 90 to 45
Calculation steps:
[( 45 - 90 ) ÷ 90] x 100 = -50%
Formula
Percentage change = [(45 - 90) / 90] x 100
Subtract the new number by the original number
45 - 90 = -45
-45 ÷ 90 = -0.5
-0.5 x 100 = -50%
Example