Can you elaborate more on the question please?

you can discount down percentages or regular discount.
they are different things.

if a dress cost 100 normally, and it is on sale for 80,
then it is 80% of its normal price.
100(.80) = 100(80/100) = 80.
if a dress is on sale at 80 and you miss the sale,
the price goes back up to normal and you pay 100
what is the discount you paid.
100/80 = 125. So you paid 25% more than it would have been on sale.

so to review :
100 to 80 is 100-80 or a 20% discount down, but a 80 to 100 change is 25% up.
20 is 20% of 100, but 20 is 25% of 80.