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Rolling to score (Posted on 2010-11-15) Difficulty: 4 of 5
We roll five standard dice (sides numbered 1 to 6) and write down the sum of the top three i.e. of the 3 highest values.
What is the probability to get 15 ?

No Solution Yet Submitted by Ady TZIDON    
Rating: 3.3333 (3 votes)

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re(2): Solution contradicting all previous ones | Comment 15 of 17 |
(In reply to re: Solution contradicting all previous ones by Charlie)

BTW, The correct formula for permutations of n objects where there are repeats among them is n! / (a!*b!*...) where a and b etc. are the number of occurrences of the repeats. For example, when taking the permutations of 2,2,5,5,5, that's 5!/(2!*3!), or 120 / (2*6) = 120 / 12 = 10. In this case, this happens to be the same as Combinations of 5 taken 2, as we are choosing 2 out of 5 to be 2's.  But it is a permutation as it accounts for all the rearrangements 22555,25255, etc.
  Posted by Charlie on 2011-04-02 17:29:27

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