1. MAN: How many birds and how many beasts do you have in your zoo?
ZOOKEEPER: There are 30 heads and 100 feet.
MAN: I can't tell from that.
ZOOKEEPER: Oh, yes you can!
2. A traveller comes to a fork in the road and does not know how to reach her destination. There are two men at the fork, one of whom always tells lies, while the other always tells the truth. The traveller doesn't know which one is which. She may ask one of the men only one question to find her way. What is her question and which man does she ask?
3. Three boxes are labelled "Apples," "Oranges," and "Apples and Oranges." Each label is incorrect. You may select only one fruit from each box. (No feeling around or peeking permitted.) How can you label each box correctly?
4. A missionary visits an island where two tribes live. One tribe always tells the truth. The other always lies. The truth tellers live on the western side of the island and the liars live on the eastern side of the island. The missionary's problem is to determine who tells the truth by asking one native only one question.
The missionary, seeing a native walking in the distance, asks a nearby native: "Go ask that native in the distance which side of the island he lives on." When the messenger returns he answers: "He lives on the western side of the island." Is the messenger a truth teller or a liar? How can you be sure?
5. You have 10 gray socks and 20 blue socks in your bureau drawer. If you reach into it in the dark, how many socks must you take out to be sure of having a pair that matches?