-50% is the change from 842 to 421
Calculation steps:
[( 421 - 842 ) ÷ 842] x 100 = -50%
Formula
Percentage change = [(421 - 842) / 842] x 100
Subtract the new number by the original number
421 - 842 = -421
-421 ÷ 842 = -0.5
-0.5 x 100 = -50%
Example