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November 08, 2025, 05:20:43 am
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Author Topic: Need a quick 101 on combinatorics  (Read 569 times)  Share 

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Daenerys Targaryen

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Need a quick 101 on combinatorics
« on: November 22, 2012, 09:06:28 pm »
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Well I'm trying to help some of my mates doing this and I have no idea what it is!
I know how to do factorials but none of this others stuff :S

If anyone could give me a quick 101 on it that would be great: just the formulas and such will suffice!


This was one of the questions I was asked: "The letters of the word MUSICAL are to be arranged in a circle. If the letters U and S must not be together, the number of possible arrangements is"

I did 6! - 2*5! and got 480 which was the answer, but have no idea why I did that.

Any help is hugely appreciated! :)
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I am Daenerys Stormborn of House Targaryen, the Unburnt, Mother of Dragons, Khaleesi to Drogo's riders, and queen of the Seven Kingdoms of Westeros
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Re: Need a quick 101 on combinatorics
« Reply #1 on: November 23, 2012, 11:01:05 am »
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if you arrange n objects in a circle, the total number of combinations is , so if you put U and S together (treat them as one object) - you now have a total of 6 objects, the total number of arrangements if U and S must be placed together is (there are two ways U and S can be arranged - U then S or S then U)

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