-70% is the change from 50 to 15
Calculation steps:
[( 15 - 50 ) ÷ 50] x 100 = -70%
Formula
Percentage change = [(15 - 50) / 50] x 100
Subtract the new number by the original number
15 - 50 = -35
-35 ÷ 50 = -0.7
-0.7 x 100 = -70%
Example