-90% is the change from 20 to 2
Calculation steps:
[( 2 - 20 ) ÷ 20] x 100 = -90%
Formula
Percentage change = [(2 - 20) / 20] x 100
Subtract the new number by the original number
2 - 20 = -18
-18 ÷ 20 = -0.9
-0.9 x 100 = -90%
Example