-97.88% is the change from 991 to 21
Calculation steps:
[( 21 - 991 ) ÷ 991] x 100 = -97.88%
Formula
Percentage change = [(21 - 991) / 991] x 100
Subtract the new number by the original number
21 - 991 = -970
-970 ÷ 991 = -0.9788092835519677
-0.9788092835519677 x 100 = -97.88%