Logic Puzzles

Bulbs

This is one of my favorite free printable logic puzzles with a real life solution.
Imagine you are in a room with 3 switches. In an adjacent room there are 3 bulbs (let's say in lamps which are on a regular table), each switch belongs to one bulb. All are off at the moment. It is impossible to see from one room to another. No help from anybody else is allowed.
How can you find out which switch belongs to which bulb, if you may enter the room with the bulbs only once?

Ball in a Hole

A table tennis ball (= a ping pong ball) fell into a tight deep pipe - it is about 30 cm long, buried in concrete pavement, having firm metal bottom, only 1 cm of the pipe is above the ground so it can not be moved. The pipe was only a bit wider then the ball, so you can not use your hand.
How would you take it out, with no damage?

The Man in the Elevator

A man lives on the tenth floor of a building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets into the elevator, and, if there is someone else in the elevator - or if it was raining that day - he goes back to his floor directly. Otherwise, he goes to the seventh floor and walks up three flights of stairs to his apartment. How come?
(This is probably the best known and most celebrated of all lateral thinking logic puzzles. It is a true classic. Although there are many possible solutions which fit the initial conditions, only the canonical answer is truly satisfying.)

Ball

How can you throw a ball as hard as you can and have it come back to you, even if it doesn't hit anything, there is nothing attached to it, and no one else catches or throws it?

Magnet

This is a logic puzzle published in Martin Gardner's column in the Scientific American.
You are in a room where there are no metal objects except for two iron rods. Only one of them is a magnet.
How can you identify this magnet?

Castle

A square medieval castle on a square island was under siege. All around the island, there was a 10 metre wide water moat. But the conquerors could make foot-bridges only 9.5 metres long. Nevertheless a wise man was able to figure out how to get over the water.
What do you think was his advice?
(There's a place on the other side to put the bridge against, not just a sheer wall. the water moat has square corners - that section of the moat is about 14.1 metres wide.)

Biology

Let's say some primitive organisms divide themselves every minute in two equal parts that are the same size as the original organism, and which also divide the next minute and so on. The saucer in which we started observing this process was full at 12.00.
When was it half full?

Sheikh's Heritage

An Arab sheikh tells his two sons to race their camels to a distant city to see who will inherit his fortune. The one whose camel is slower will win. The brothers, after wandering aimlessly for days, ask a wise man for advice. After hearing the advice they jump on the camels and race as fast as they can to the city.
What does the wise man say?

Philosopher's Clock

This is an old logic puzzle. One philosopher had a clock, which he had forgotten to wind up. He had no other clock, watch, radio, TV, phone or any other device telling the time. So when his clock stopped he went to a friend (road from one house to another is flat plane only), stayed there the whole night and when he came home, he knew the right time.
How could he know?

Masters of Logic Puzzles (dots)

Three masters of logic wanted to find out who was the wisest one. So they invited the grand master, who took them into a dark room and said: "I will paint each one of you a red or a blue dot on your forehead. When you walk out and you see at least one red point, raise your hands. The one who says what colour is the dot on his own forehead first, wins." Then he painted only red dots on every one. When they went out everybody had their hands up and after a while one of them said: "I have a red dot on my head."
How could he be so sure?

Masters of Logic Puzzles II. (hats)

The two losing masters wanted a riposte against the winning master, so the grand master showed them 5 hats, two white and three black. Then he said: "I will turn off the light and put a hat on each of your heads and hide the other hats. When I turn on the light you will have equal chances to win. Each of you will see the hats of the two others, however not his own. The first one saying the colour of his hat will win." Then before he could turn off the light, one of the masters (the same one again) guessed, what the colour of his hat will be.
What hat was it and how did he know?

Masters of Logic Puzzles III. (stamps)

Try this. The grand master takes a set of 8 stamps, 4 red and 4 green, known to the logicians, and loosely affixes two to the forehead of each logician so that each logician can see all the other stamps except those 2 in the moderator's pocket and the two on her own head. He asks them in turn if they know the colors of their own stamps:
A: "No."
B: "No."
C: "No."
A: "No."
B: "Yes."
What are the colors of her stamps, and what is the situation?

Head Bands

Three white men were taken captive by a hostile Indian tribe. The chieftain was willing to let them go so he took them to a tepee, where there was no light. He put one head band on each of their heads (he had 3 white and 2 red - so 2 head bands were not used). Then they went out in a queue so that each man saw the head-band of those standing in front of himself (the first one did not see any head band, the second one saw the first one's head band, and the third one saw the head bands of the two others). If somebody said the colour of his head-band, they all would be free. After a quiet while one of them said: "My head-band is ...".
What colour was his head band? And how would you reason it?

Further conditions:
You have to assume that all the prisoners are fairly intelligent and have confidence in the intelligence of their fellow prisoners.
An incorrect guess deems them to imprisonment.
Only one guess can be made by the group.

Christmas Tree

There were 4 angels on a Christmas tree (besides other frou-frou). Two had a blue aureole and two yellow, however none of them can see behind his head. Angel A is on the highest place and he can see angels B and C, which hang below him. Below hangs angel B, who can see only angel C under him. Angel C can't see anybody, because angel D hangs under a twig (nobody can see him and he can not see anyone either).
Which one of them will be the first to speak his guess out load (deduce and say) what his own aureole is?