At a yard sale, you find a number of paperback books by your favorite author. You have $10 in each book is priced at $.75. Write a rule for the amount of money you have left as a function of the number of books you buy.

Assume that the number of books you buy is n.

Now since each book costs 0.75$ and you buy n books, therefore, the total amount you pay for all the books can be calculated as follows:

total amount paid = $0.75n

Now, you have 10$ and you have paid $0.75n for the books.

Based on this, the amount of money left can be calculated as follows:

amount of money left = 10 - 0.75n