-21% is the change from 100 to 79
Calculation steps:
[( 79 - 100 ) ÷ 100] x 100 = -21%
Formula
Percentage change = [(79 - 100) / 100] x 100
Subtract the new number by the original number
79 - 100 = -21
-21 ÷ 100 = -0.21
-0.21 x 100 = -21%
Example