-70% is the change from 70 to 21
Calculation steps:
[( 21 - 70 ) ÷ 70] x 100 = -70%
Formula
Percentage change = [(21 - 70) / 70] x 100
Subtract the new number by the original number
21 - 70 = -49
-49 ÷ 70 = -0.7
-0.7 x 100 = -70%
Example