950% is the change from 40 to 420
Calculation steps:
[( 420 - 40 ) ÷ 40] x 100 = 950%
Formula
Percentage change = [(420 - 40) / 40] x 100
Subtract the new number by the original number
420 - 40 = 380
380 ÷ 40 = 9.5
9.5 x 100 = 950%
Example