Logic Riddles

Played poker with a guy named Barry tonight. He owns a pretty big trading firm in Chicago that screens thousands of college grads each year to see if they are a good fit to be a trader. Apparently the interview process includes these odd logic puzzles to see how you think on your feet. He gave me a few tonight that were interesting to think about: (Try to answer each question in 5 minutes time, goal is to create an answer that makes some sense)

1. There are three 1 pound balls that need to be carried over a bridge. The bridge can only hold a total weight of you + 2 balls. Your task is to transport all 3 balls across the bridge in one trip. How do you do it?

2. A man works on the 50th floor. When he starts work, he takes the elevator to the 18th floor, then uses the stairs to walk up the remaining 32 floors. On the way back home, he takes the elevator all the way down. Why does he do this?

3. You find a man lying dead in the desert. There is nothing around him. You know what killed him, and you know exactly what he was doing before he died. What was he doing before he died and what killed him?

4. If I told you that I could flip a coin and pick heads or tails correctly 2 out of every 3 coin flips, what odds would you lay me?

5. Using only one mathematical symbol, and all the numbers between 0 and 9 (once and without repeating) make the equation equal 99.

And now for the harder ones that you can take your time with.

6. There are 3 light switches outside of a room. One of the switches is connected to a light bulb inside the room. Each of the three switches can be either 'ON' or 'OFF'. You are allowed to set each switch the way you want it before entering the room. Once you enter the room the door will lock you inside until you can determine which switch controls the bulb. How do you figure out which switch controls the bulb?

7. Mr. Black, Mr. Gray, and Mr. White are fighting in a truel. They each get a gun and take turns shooting at each other until only one person is left. Mr. Black, who hits his shot 1/3 of the time, gets to shoot first. Mr. Gray, who hits his shot 2/3 of the time, gets to shoot next, assuming he is still alive. Mr. White, who hits his shot all the time, shoots next, assuming he is also alive. The cycle repeats. If you are Mr. Black, where should you shoot first for the highest chance of survival?


Post others if you guys find more interesting ones.

5.
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2.
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wild guess on 1
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Read in Scottish accent (more fun lol)
Four old Vikings have only one lit torch. They are standing besides a narrow bridge in the middle of the night after a long day of battle, the bridge only holds two big Vikings at a time so to get home they must cross the bridge two at a time.
Each of them are wounded differently so their crossing time over the bridge is not equally long:

Viking A is rather healthy, it takes him 5 minutes to cross the bridge
Viking B is wounded, it takes him 10 minutes to cross the bridge
Viking C is wounded, it takes him 20 minutes to cross the bridge
Viking D is badly wounded, it takes him 25 minutes to cross the bridge

It is so dark that they cannot see unless one Viking carries the lit torch that they have over the bridge.
e.g. if A and C travel together over, their time would be 20 minutes and someone would have to bring the torch back to B and D waiting on the other side.

What is the shortest time for all of them to cross the bridge and get home safe and sound? And in what order should they go?

4.
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Odds of guessing 3 out of 3 is: 1/8

Eight different results:

Odds of guessing 2 out of 3 is: Right Wrong Right
Wrong Right Right
Right Right Wrong = 3/8 = 37,5%
To be +EV you should lay someone lower odds than 3/8

Right or wrong ?

On October 18 2012 09:25 TeSpartan wrote: Read in Scottish accent (more fun lol) Four old Vikings have only one lit torch. They are standing besides a narrow bridge in the middle of the night after a long day of battle, the bridge only holds two big Vikings at a time so to get home they must cross the bridge two at a time. Each of them are wounded differently so their crossing time over the bridge is not equally long: Viking A is rather healthy, it takes him 5 minutes to cross the bridge Viking B is wounded, it takes him 10 minutes to cross the bridge Viking C is wounded, it takes him 20 minutes to cross the bridge Viking D is badly wounded, it takes him 25 minutes to cross the bridge It is so dark that they cannot see unless one Viking carries the lit torch that they have over the bridge. e.g. if A and C travel together over, their time would be 20 minutes and someone would have to bring the torch back to B and D waiting on the other side. What is the shortest time for all of them to cross the bridge and get home safe and sound? And in what order should they go?

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2 is easy. Player999 got it.

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ok went through them and wrote down thought process


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question 4 he means what odds to give him that he gets one single flip right, answers above are off
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1. Build a raft.

2. The elevator broke on his way up.

3. If I already know, doesn't that defeat the purpose of the question?

4. I wouldn't lay you any because the coin is probably rigged.

5. im bad at math!!! ...

ill post the others after thinking

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Popularish but one of my favs:
You are at a cross road, and you see two kids playing. One of them always tells the truth, the other always lies. You don't know which one is which.

You get to ask one question to one of them find out the correct direction.

On October 18 2012 13:47 Moksha wrote: 1) + Show Spoiler + a) bowling-roll 1 ball to otherside b) walk across with the 2 remaining balls c) ??? d) PROFIT!!!1 Popularish but one of my favs: You are at a cross road, and you see two kids playing. One of them always tells the truth, the other always lies. You don't know which one is which. You get to ask one question to one of them find out the correct direction.

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On October 18 2012 13:47 Moksha wrote: 1) + Show Spoiler + a) bowling-roll 1 ball to otherside b) walk across with the 2 remaining balls c) ??? d) PROFIT!!!1 Popularish but one of my favs: You are at a cross road, and you see two kids playing. One of them always tells the truth, the other always lies. You don't know which one is which. You get to ask one question to one of them find out the correct direction.

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1. How big is the bridge?

2. Exercise

3. He was doing the thing that killed him, and he died because he was doing that.

4. I would lay you 1:100. No, 1:1000. Fuck it, 1:1000000000. I will lay you the lowest possible odds I can convince you to take.

5. 12345678 = 99. I used the numbers between 0 and 9, and I made them equal 99. The equal symbol itself is a mathematical symbol.

6. Turn 2 switches on. Then randomly guess which of the 2 is the light. It's worth the 50/50 gamble plus you might get lucky and the light will still be off when you enter. There's no guarantee the bulb will be accessible to touch, and some bulbs dont produce a perceptible level of heat.

7. Forfeit your turn and shoot into the air. You cant risk #3 living and killing you, you need to let #2 have his chance first. Upon seeing this they are likely to duel each other giving you more time. Then just roll the dice and try to kill whoever is left.


At first these answers might seem silly, but the goal is to be pragmatic. Usually these kinds of questions are meant to assess your line of thinking, not get a correct answer, since obviously there can be no correct answer most of the time. I've heard of interviewers asking questions like "how many golf balls could fill this room?" and "explain a database to your 5 year old nephew in 3 sentences". It's a personality test.