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Director
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combinations [#permalink] New post 25 Apr 2006, 09:29
just a refresher,

how many ways could you arrange the following letters? how do you approach these types agian? thanks
1)AABB

2)ABCDEF

3)AABBCC

4)AAB
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Re: combinations [#permalink] New post 25 Apr 2006, 09:42
joemama142000 wrote:
just a refresher,

how many ways could you arrange the following letters? how do you approach these types agian? thanks
1)AABB 4!/(2! *2!)

2)ABCDEF 6!

3)AABBCC 6! /(2! *2! *2!)

4)AAB3!/2!



to solve these kinds of problem first count the total no of alphabets say N and in the numerator put N! and if some of them are repeated r1 times , and some other r2 times ........divide the numerator by those factorial . so it becomes N!/(r1! *r2!)
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 [#permalink] New post 25 Apr 2006, 10:07
joemama142000 wrote:
thanks ipc


you are always welcome .
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 [#permalink] New post 25 Apr 2006, 11:32
a real refresher .. indeed!
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 [#permalink] New post 25 Apr 2006, 17:44
thanks a lot!

that was a good refresher!
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 [#permalink] New post 25 Apr 2006, 17:56
1)AABB
Number of ways to arrange any 4 letters = 4!
But A and B are repeated, so we need to consider that there are going to be duplicates. The total number of ways is therefore 4!/2!2! = 6 ways

2)ABCDEF
The number of ways to arrange this is 6! simply because each letter is a different entity.

3)AABBCC
The way to approach this is the same as explained in 1. It's 6!/2!2!2! = 90 ways.

4)AAB
Same as for 3. Number of ways = 3!/2! = 3
  [#permalink] 25 Apr 2006, 17:56
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