Answer:
2 for $420
Explanation:
You want to know which deal for hardcover books is the most attractive.
Books
The deal that is best depends on the number of books you need.
If you need 1 book, then one for $250 is the lowest price you can get.
If you need 2 books, then two for $420 is the lowest price you can get. This price point has the lowest cost per book, but if you just need one book you will be paying $170 more than necessary.
The price per book is lowest with the "two for $420" deal.
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Additional comment
The purpose of pricing like this is to get you to buy more than you need. It increases the seller's revenue, but can result in expensive waste.
If you need 3 books, the quarter-dozen price is the best.
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