-50% is the change from 340 to 170
Calculation steps:
[( 170 - 340 ) ÷ 340] x 100 = -50%
Formula
Percentage change = [(170 - 340) / 340] x 100
Subtract the new number by the original number
170 - 340 = -170
-170 ÷ 340 = -0.5
-0.5 x 100 = -50%
Example