Abookstore has a sale: jen wants to buy four books: for $10.00, for $12.00, for $15.00, and for $20.00. what is the smallest she could pay for these books during the sale? by what percent would the sale reduce the total cost of these four books?

$47, 17.5%

Step-by-step explanation:

When she buys the $20 book, she can get 40% off either the $15, $12, or $10 book.  She'll save the most by getting 40% off the $15 book.

Then, when she buys the $12 book, she'll get %40 off the $10 book.

The total she pays is:

20 + (0.60)(15) + 12 + (0.60)(10)

20 + 9 + 12 + 6

47

Without the discounts, the cost of the books would have been:

20 + 15 + 12 + 10

57

So she saves $10.  10 out of 57 is approximately 17.5%.