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Ferihere
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GMATPrep 2: Question 24 18 Sep 2007, 09:46
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My weakness....



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dahcrap
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GMATPrep 2: Question 24 18 Sep 2007, 09:48
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The answer is 26 + 26^2 + 26^3
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Ferihere
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GMATPrep 2: Question 24 18 Sep 2007, 09:52
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dahcrap
The answer is 26 + 26^2 + 26^3
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Can you explain or give a source which may provide explanation for this kind of problems, probabilities???
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GMATBLACKBELT
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GMATPrep 2: Question 24 18 Sep 2007, 10:28
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Howd, u get C?

I get E. 26 for first one. 26*26 for second one. 26*26*26 for third one.

or 26+26^2+26^3---> 26+676+17576=18278.


Wuts the OA?
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r019h
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GMATPrep 2: Question 24 18 Sep 2007, 12:02
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dahcrap
The answer is 26 + 26^2 + 26^3
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yep thats my answer as well. what is OA?
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GMAThopefull
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GMATPrep 2: Question 24 18 Sep 2007, 21:08
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yup that's what I got as well.

although I, in order to save time, calculated 26 ^ 3 first and the result was greater than choice D. In the actual exam, I'd choose E immediately and move on.
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GMATPrep 2: Question 24 18 Sep 2007, 21:14
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dahcrap
The answer is 26 + 26^2 + 26^3

Can you explain or give a source which may provide explanation for this kind of problems, probabilities???
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One Letter codes:
@

26 letters = 26 codes

Two Letter codes:
@#

@ can be one of 26 letters. # can be one of 26 letters. It's a permutation. Question specifically mentions that repetitions are allowed (i.e. code: JJ is valid).

as a result we have 26 * 26 choices.

Three letter codes:

same as two letter codes. 26 * 26 * 26

once you add all of them, you get choice E. Of course, as I mentioned above, the best way to save time is that as soon as you realize the solution, you start from the biggest number and go on from there. In this case, whoever does 26^ 3first, saves time by not having to do the other two. This is because 26 ^3 is bigger than all other choices except E.




Also note that if repetitions weren't allowed calcuation would then be: 26 + 26*25 + 26 * 25 * 24

hope this helps.
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GMATPrep 2: Question 24 20 Sep 2007, 08:30
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You are tight guys/girls OA is E

Can you give me some useful source about this topic???



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