-50.16% is the change from 642 to 320
Calculation steps:
[( 320 - 642 ) ÷ 642] x 100 = -50.16%
Formula
Percentage change = [(320 - 642) / 642] x 100
Subtract the new number by the original number
320 - 642 = -322
-322 ÷ 642 = -0.5015576323987538
-0.5015576323987538 x 100 = -50.16%