-50% is the change from 672 to 336
Calculation steps:
[( 336 - 672 ) ÷ 672] x 100 = -50%
Formula
Percentage change = [(336 - 672) / 672] x 100
Subtract the new number by the original number
336 - 672 = -336
-336 ÷ 672 = -0.5
-0.5 x 100 = -50%
Example