-50% is the change from 240 to 120
Calculation steps:
[( 120 - 240 ) ÷ 240] x 100 = -50%
Formula
Percentage change = [(120 - 240) / 240] x 100
Subtract the new number by the original number
120 - 240 = -120
-120 ÷ 240 = -0.5
-0.5 x 100 = -50%
Example