Answer:
$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%.
