A book costs $25. Marilyn bought the book during a sale with 15% discount. How much did she pay for the book

Original cost of the book = $25

Percentage of discount got by Marilyn while buying the book = 15%

Amount of discount got by Marilyn while buying the book = (15/100) * 25

= 375/100

= 3.75 dollars

So

The amount paid by Marilyn for buying the book = (25 - 3.75) dollars

= 21.25 dollars

So the total amount paid by Marilyn for buying the book is $21.25. I hope the procedure for doing this problem is clear to you.