-15% is the change from 20 to 17
Calculation steps:
[( 17 - 20 ) ÷ 20] x 100 = -15%
Formula
Percentage change = [(17 - 20) / 20] x 100
Subtract the new number by the original number
17 - 20 = -3
-3 ÷ 20 = -0.15
-0.15 x 100 = -15%
Example