If a book costs $15 and is on sale for 20% off, what is the sale price?

To determine the sale price of the book, you need to first calculate the amount of the discount and then subtract that discount from the original price.

The original price of the book is $15. The discount is 20% of that price. To find 20% of $15, you can multiply $15 by 0.20:

[

15 \times 0.20 = 3

]

This means the discount amount is $3. To find the sale price, you subtract the discount from the original price:

[

15 - 3 = 12

]

Thus, the sale price of the book after applying the discount is $12. This is the correct answer, as it accurately reflects the calculation of the discount and the resulting price of the book after the sale.