-50.08% is the change from 639 to 319
Calculation steps:
[( 319 - 639 ) ÷ 639] x 100 = -50.08%
Formula
Percentage change = [(319 - 639) / 639] x 100
Subtract the new number by the original number
319 - 639 = -320
-320 ÷ 639 = -0.5007824726134585
-0.5007824726134585 x 100 = -50.08%