Tag Archives: probability

Birthday simulations using Python and Numpy

Posted on August 26, 2010 by nolfonzo

I’ve written previously about the probability of finding a shared birthday in a room full of people. I wanted to run some simulations on this using Python. As an aside, you’ll find some of the techniques below bear a similarity … Continue reading →

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Birthday pairings

Posted on April 30, 2010 by nolfonzo

Here’s two classic birthday puzzles: How many people do you need in a room to have a better than 50% chance of finding at least one shared birthday among them? How many people do you need in a room with … Continue reading →

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A perfect hand, with some combinatorial tricks

Posted on April 29, 2010 by nolfonzo

Question: You deal the first 13 cards from a well shuffled, 52-card deck. What are the chances the 13 cards you deal are of the same suit? There’s a couple of ways to do this – both incorporate useful techniques … Continue reading →

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Alternating coin toss – redux

Posted on April 10, 2010 by nolfonzo

I want to revisit a probability puzzle from a previous post: see Alternating coin toss game. You play a game where you alternate tossing a coin with a friend, and the first person to toss heads wins. But let’s make … Continue reading →

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Puzzle – Take your seats

Posted on April 7, 2010 by nolfonzo

Another problem that has an immediate intuitive answer, but can be tricky if you don’t have that insight. Question Let’s say there are 100 people, including you, waiting to board a fully booked flight, each with an assigned seat. The … Continue reading →

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Puzzle – Liars and Truthtellers

Posted on December 31, 2009 by nolfonzo

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 – Roll a die for $

Posted on June 2, 2008 by nolfonzo

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

Posted on June 1, 2008 by nolfonzo

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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