-47.5% is the change from 800 to 420
Calculation steps:
[( 420 - 800 ) ÷ 800] x 100 = -47.5%
Formula
Percentage change = [(420 - 800) / 800] x 100
Subtract the new number by the original number
420 - 800 = -380
-380 ÷ 800 = -0.475
-0.475 x 100 = -47.5%