Stephen M.

asked • 05/11/19

What is the probability that after rolling a fair, six-sided die N times, exactly two different numbers (only) will show up in the sequence?

1 Expert Answer

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Patrick B. answered • 05/11/19

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Stephen M.

No, that’s definitely incorrect as it includes cases in which only one number shows up repeatedly. Although I asked the question for runs of two numbers, I’m really interested in the general case of runs of M numbers, (1<=M<=6), and in fact the more general case of dice with any number of sides S, where S > 1.
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05/11/19

Stephen M.

Here’s some more information: I directly computed the probabilities for rolling runs of two numbers by exhaustively calculating the possibilities, for various rolls of dice. For N = 1, p = 1.000 (obviously). For N = 2, p = 0.833. For N = 3, p = 0.417. For N = 4, p = 0.162. For N = 5, p = 0.058. And for N = 6, p = 0.020. I’d like a general formula.
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05/12/19

Stephen M.

Oops! Obviously, for N = 1, the probability isn’t 1.000, since it can’t happen!
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05/12/19

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