-50% is the change from 78 to 39
Calculation steps:
[( 39 - 78 ) ÷ 78] x 100 = -50%
Formula
Percentage change = [(39 - 78) / 78] x 100
Subtract the new number by the original number
39 - 78 = -39
-39 ÷ 78 = -0.5
-0.5 x 100 = -50%
Example