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 Post subject: Combinatorics and Probabilities Q 21Posted: Tue Jan 31, 2012 9:48 am

Joined: Mon Jan 02, 2012 4:25 am
Posts: 2
In Q21 they are talking about two-element subsets. I had no idea what they meant.

So in the answer it states that there are 6 two-element subsets??

Could you explain what they mean and why there are 6?

Thanks

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 Post subject: Re: Combinatorics and Probabilities Q 21Posted: Tue Jan 31, 2012 4:59 pm

Joined: Thu Feb 12, 2009 6:32 pm
Posts: 497
By "two element subsets" we mean sets made of of two of the four numbers in the original set : {1, 2, 3, 4}

There are "4 choose 2" of these: (4! / (2! * (6-2)!) = 4*3/(2*1) = 6

one of these {2,4} contains 2 and 4, so the the answer is 6 - 1 = 5

- Veritas Help

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