Tag Archives: puzzles

Puzzle – Leaning Tower of Pisa

Let’s say you drop a ball from the Leaning Tower of Pisa, which is 179 ft high, and it bounces back 10% of the dropped height – 17.9 ft. Then on the second bounce it bounces up 10% again – … Continue reading

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Puzzle – Break a stick to get a triangle

I read somewhere this is a Google interview question: Let’s say you drop a stick, breaking it randomly in 2 places, leaving you with 3 smaller sticks.   What’s the probability you can make a triangle out of the 3 resulting … Continue reading

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Puzzle – 4 Bugs chasing each other

The answer to this problem is either really obvious, or it’s not. Say there are four bugs standing at the corners of an imaginary 1m * 1m square.  Each of the bugs is facing the bug that is on the … Continue reading

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Puzzle – Liars and Truthtellers

This is another probability question that seems straightforward but can be deceptive… You’re an FBI agent and have been monitoring a large gang, and you know that 1/4 of its members always tell the truth, the rest always lie.  Then … Continue reading

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Puzzle – shortest road system

Let’s say you’re contracted to build roads to connect four towns that are at the corners of an imaginary square with sides 1 mile. What’s the shortest length of road system you can build so that every town can get … Continue reading

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Puzzle – Clock

It’s 3 O’Clock. What will be the time when the minute and hour hands are next in the same position (coincident)? One way to solve this problem:  start with the minute hand at the 12 and hour hand at the … Continue reading

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More puzzles…

Some of these are from Heard on the Street – a book of interview questions for Quants I’m trying to get through. Well worth a read if you’re into this sort of thing… 1. Two ropes of different lengths, and … Continue reading

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Puzzle – Alternating coin toss game

A really simple problem, but needs a trick or two to solve quickly. Question: You take it in turns tossing a coin with a friend – you having the first toss – and keep going until one of you tosses … Continue reading

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Puzzle – Roll a die for $

This is an interesting puzzle in that it shows a basic technique used in solving these kinds of probability puzzles, as well as in models for some derivatives pricing, without the need for conditional probability calculations. Hint: start with the … Continue reading

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Classic Probability Puzzles

1. I have two children. One of my children is a girl. What are the chances I have two girls? The answer to this question is not 50/50. After being told that one of your children is a girl, you … Continue reading

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