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Archive for July, 2010

There’s an intriguing little math puzzle that can be used to position yourself as smarter than everyone around you — even if you’re not good at math. It’s the Tuesday Child Puzzle, which I came across recently. The question is simple enough:

If I have two children and one of them is a boy born on Tuesday, what are the odds that my other child is also a boy?

This question is nice because most everyone gets it wrong initially, even people who are normally good at math. You can go to this blog posting and study the details. But here, in addition to giving an alternate way to see the answers, I’ll give important recommendations for the most effective way to present this puzzle to others, to maximize both your fun and their humiliation.

First, note that the answer is not 50% (it’s a little less, 13 out of 27) But it’s a very safe bet that 50% is what you will hear. Here’s an excel file that contains my solution — no real programming required in this case (it also lets you experiment with variations on the question, like allowing for a boy born on Tuesday, Wednesday, or Friday).

So, on to the recommended delivery. A meal setting is preferred, one that allows you access to something to drink.

You (with glass of water in hand): “Hey here’s a question. If I have two children, and one is a boy born on a Tuesday, what are the chances that the other child is also a boy?”

Quickly drink some water but do not swallow yet.

Them: “Um, it’s 50% isn’t it?” [or, “I don’t see what the day has to do with it. It’s 50%.”]

You: Spit out the water suddenly as you start and then stifle a rapid laugh of apparent surprise. “Oh sorry,” you say, gasping and wiping your moJust after they say 50%uth, hopefully also with them having to clean some of the water off themselves. “Yea, I guess that one was a little hard. Here’s the easier version for you: Let’s say I have two children and one is a boy born on any day of the week. What are the chances the other one is a boy this time?”

At this point you rapidly reload water into your mouth, and then look at them with an inquisitive look like you’re expecting another answer.

The answer to this question is again not 50% (it’s 1 in 3, 33%). But this time they may not answer so rapidly. If they (wisely) won’t answer, then if you don’t understand the mechanics of the puzzle, just tell your audience to think about it and you’re sure they’ll figure it out eventually. And say this with a careful delivery of humble smugness.

Enjoy this fun community puzzling activity. For extra credit, experiment with different liquids.

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