-30% is the change from 100 to 70
Calculation steps:
[( 70 - 100 ) ÷ 100] x 100 = -30%
Formula
Percentage change = [(70 - 100) / 100] x 100
Subtract the new number by the original number
70 - 100 = -30
-30 ÷ 100 = -0.3
-0.3 x 100 = -30%
Example