-49.4% is the change from 830 to 420
Calculation steps:
[( 420 - 830 ) ÷ 830] x 100 = -49.4%
Formula
Percentage change = [(420 - 830) / 830] x 100
Subtract the new number by the original number
420 - 830 = -410
-410 ÷ 830 = -0.4939759036144578
-0.4939759036144578 x 100 = -49.4%