I was interested enough in this problem that I Googled to see what the question was, thought about it, and when I didn't solve it in ten seconds or so, looked up the answer. Would I have solved it? Yeah, eventually. But what this question tells me is the difference between learning some mathematics and thinking mathematically. If you've just memorized some formulae, you're going to be thrown off by the two parts of the question. But if your approach to probabilities is to automatically set up the (correct) formula, you can actually solve this in your head in a couple of seconds. Can you show that (6/n)*(5/n-1)=1/3 means (n^2)-n-90=0? Sure, easily.

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Last Updated: Apr 26, 2017 04:53 a.m.