-50% is the change from 638 to 319
Calculation steps:
[( 319 - 638 ) ÷ 638] x 100 = -50%
Formula
Percentage change = [(319 - 638) / 638] x 100
Subtract the new number by the original number
319 - 638 = -319
-319 ÷ 638 = -0.5
-0.5 x 100 = -50%
Example