5% is the change from 400 to 420
Calculation steps:
[( 420 - 400 ) ÷ 400] x 100 = 5%
Formula
Percentage change = [(420 - 400) / 400] x 100
Subtract the new number by the original number
420 - 400 = 20
20 ÷ 400 = 0.05
0.05 x 100 = 5%
Example