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How many letter combinations can be composed of letters of

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How many letter combinations can be composed of letters of [#permalink] New post 06 Nov 2008, 10:11
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

43% (01:13) correct 57% (00:29) wrong based on 5 sessions
How many letter combinations can be composed of letters of the word LEVEL if all these combinations have to begin with L and end with E?

* 4
* 6
* 10
* 12
* 24
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Re: Combinations [#permalink] New post 06 Nov 2008, 10:44
so u r changing three places within the LEVEL

1x2x3=6

B
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Re: Combinations [#permalink] New post 07 Nov 2008, 05:53
How many letter combinations can be composed of letters of the word LEVEL if all these combinations have to begin with L and end with E?


Not really
LEVEL
L - L1
E - E1
V - V
E - E2
L - L2

Since the Es and Ls could be either of the two, we have four options -
Ist-----------Last
L -----------E
L1 -----------E1
L -----------E
L1 -----------E1

The center 3 have - 6 - combinations

Hence the total ways the letters can be arranged is 24
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Re: Combinations [#permalink] New post 07 Nov 2008, 06:27
How do you differentiate between the same letter L? I thought about the number of ways of picking one L and one E out of 2 L's and 2 E's respectively.

Write down and see if you really get 24. In the end L1=L2 & E1=E2 and your combinations will reduce down to 6
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Re: Combinations [#permalink] New post 08 Nov 2008, 03:45
Ah! you are right icandy - thanks.
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Re: Combinations [#permalink] New post 22 May 2010, 21:53
Can somebody elaborate on this problem,
I can not get which method you guys are using to come to the solution.

Slot method or using specific combinatorics formula?

My thinking was that Letter L could be chosen in two ways, Letter E in 2 ways as well, and the middle V only one way, thus
I am getting 4
I know it is not correct answer.
Thank you.
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Re: Combinations [#permalink] New post 23 May 2010, 02:09
Expert's post
mirzohidjon wrote:
Can somebody elaborate on this problem,
I can not get which method you guys are using to come to the solution.

Slot method or using specific combinatorics formula?

My thinking was that Letter L could be chosen in two ways, Letter E in 2 ways as well, and the middle V only one way, thus
I am getting 4
I know it is not correct answer.
Thank you.


How many letter combinations can be composed of letters of the word LEVEL if all these combinations have to begin with L and end with E?

Keep it simple:

L---E: three distinct letters are left - V, E and L. We can place them in three slots in 3!=6 # of ways (basically it's the same as # of permutations of 3 distinct letters - 3!).
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Re: Combinations [#permalink] New post 23 May 2010, 10:23
Thank you,
Now I got it!
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Re: Combinations [#permalink] New post 01 Jun 2010, 06:36
Check he differnce between the two questions

How many letter combinations can be composed of letters of the word LEVEL if all these combinations have to begin with L and end with E?

* 4
* 6
* 10
* 12
* 24

How many ways can the letter - TRUST - be arranged?

* 30
* 60
* 6
* 3
* 24

Ans to both is B
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Re: Combinations [#permalink] New post 24 Apr 2011, 08:02
Hi Bunuel,
Isn't the question ambiguous? At its current form, why should we not include word combinations which would have just one or two letters in between L and E. For example, should not LVE or LLVE be included? Dont see anything in the question which would stop us from including such combinations. Am I wrong? Please help. Thanks.
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Re: Combinations [#permalink] New post 24 Apr 2011, 10:09
neel1982 wrote:
Hi Bunuel,
Isn't the question ambiguous? At its current form, why should we not include word combinations which would have just one or two letters in between L and E. For example, should not LVE or LLVE be included? Dont see anything in the question which would stop us from including such combinations. Am I wrong? Please help. Thanks.


As I read the question, you're perfectly right - there's no reason from the wording to assume we need to use all 5 of the letters (though if you don't need to use all five letters, the right answer is not among the choices).

Perhaps worse still, the question asks how many 'combinations' we can make. In mathematics, a 'combination' is a selection *where order does not matter*. If we are creating 'words', obviously order does matter. It's crucially important that the question be clear about whether order matters here, and it isn't. The language of the question is horrible; the original post is so old I doubt we'll ever know the source, but whatever it is, I wouldn't recommend using it.
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Re: Combinations [#permalink] New post 24 Apr 2011, 17:42
Ian ,

dont we have to consider chosing one L out of two and one E out of two for the edges? how come answer is its just 6! then?

Please clarify.
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Re: Combinations [#permalink] New post 24 Apr 2011, 19:27
Spidy001 wrote:
Ian ,

dont we have to consider chosing one L out of two and one E out of two for the edges? how come answer is its just 6! then?

Please clarify.


I'm afraid I don't understand your question - what do you mean by 'edges'?
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Re: Combinations [#permalink] New post 24 Apr 2011, 20:41
i meant start and end.

we have 2 L's and 2 E's right? Let me know if this approach is right?

selecting one L out 2 * 3 distinct letter permutations * selecting one E out of 2

= 2c1 * 3! * 2c1

finally we divide this by 2! *2! for because we have 2 L's and 2 E's

= 2c1 * 3! * 2c1 / (2! *2!) = 6
Re: Combinations   [#permalink] 24 Apr 2011, 20:41
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