-90% is the change from 210 to 21
Calculation steps:
[( 21 - 210 ) ÷ 210] x 100 = -90%
Formula
Percentage change = [(21 - 210) / 210] x 100
Subtract the new number by the original number
21 - 210 = -189
-189 ÷ 210 = -0.9
-0.9 x 100 = -90%
Example