The only practical reason to calculate the discount is
as an intermediate step in determining the new price.
Chat with our AI personalities
That means that there is a discount (a price reduction, compared to the "official" price), and that this reduction is calculate as a percentage of the total price.
Cp = sp/d
The quickest way is to multiply the full price by 0.2 That is the amount of the discount.
A discount is subtracted. Suppose something's price was $5 and there was a $1 for that day. You could calculate the price by doing $5 -$1 = $4. The discount is the reduction in price.
9%