RAY: You’re given a hundred dollars and told to spend it all purchasing exactly a hundred animals at the pet store. Dogs cost $15. Cats cost a buck, and mice are 25 cents each.
TOM: Let me get this straight. You have to spend exactly a hundred bucks and you end up with exactly a hundred animals?
RAY: Right. The other only other criterion is that you have to purchase at least one of each animal.
The question is, how many of each animal do you have to purchase to equal a hundred animals purchased at exactly a hundred dollars?
(spoiler: answer is here.)
RAY: A family of four and their dog are trapped on an island, when rising floodwaters tear out the bridge that they had used just a few hours earlier. When they had just given up hope the son says, “I’ve got a small boat and oars.”
But their joy was short-lived. The manufacturer’s instructions printed on the boat stern said that the boat can carry only 180 pounds.
The dog is the only one who can swim.
The father weighs 170. The mother says she weighs 130 but it’s more like 155. The son is 90 pounds, the daughter is 80, and the dog is 15.
Here’s the question: What’s the fewest number of crossings they have to make to save everybody?
Update – 1/21/11
(spoiler – answer is here.)