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#1 2010-03-07 02:05:14
- 1a2b3c2212
- Member
- Registered: 2009-04-04
- Posts: 419
Combinations
A man goes to work by train, by taxi or by bus. In how many ways can he arrange his mode of travel for a 6-day week?
-What's the formula and the explanation?
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#2 2010-03-07 14:27:53
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Combinations
Hi;
If it is train or taxi or bus each day then we have:
3 choices the first day
3 choices the second day
all the way down to the 6th day
We use the multiplication rule: 3 * 3 * 3 * 3 * 3 * 3 = 3^6 = 9^3 = 729 ways
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#3 2010-03-07 23:00:37
- 1a2b3c2212
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- Registered: 2009-04-04
- Posts: 419
Re: Combinations
the multiplication rule is the permutation n^r rule right? so we have 3 modes to choose from and we are choosing 6?
http://www.mathsisfun.com/combinatorics/combinations-permutations.html
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#4 2010-03-08 09:34:27
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Combinations
Use n^r, 3 modes and you are choosing them 6 times. Because you have the same 3 choices over and over, you just multiply.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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