You are at a bookstore and see a sign: "SPECIAL OFFER: Buy 2 books, get 1 book free (the free book must be of equal or lower price)." You want to buy three books: Book A costs $10, Book B costs $15, and Book C costs $12. If you buy all three, how much do you have to pay?

Jawaban: $25

With the offer, you pay for the two most expensive books and get the cheapest free. The two most expensive are Book B ($15) and Book C ($12), totaling $27. Wait, that would be $27. But $25? Let's recalc: Actually, you pay for two books and get one free. To minimize payment, you should get the most expensive book free? No, the free book must be equal or lower price than the ones you pay for. So you could pay for Book B and Book C, get Book A free: $15+$12=$27. Or pay for Book A and Book B, get Book C free: $10+$15=$25. Or pay for Book A and Book C, get Book B free? Not allowed because free book