Suppose you sit in a rubber boat in a swimming pool. In the boat lies a stone. You throw this stone from the boat into the pool. Will the water level in the pool raise or drop?

You're travelling to some village. At some point there is a fork in the road. You could go two ways but only one of them leads to the village. Lucky for you there are two men standing next to the fork. But unfortunately one of them always lies and one always speaks the truth and you do not know who is who. Since the men do not really like to help you, you are allowed to ask one of them only one question. Which question should you ask?

Suppose you would like to boil an egg for exactly 15 minutes. But you only have two hourglasses, one of zeven and one of eleven minutes. What is the the fastest way to do this?