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GMATPREP:Permutaion & combination

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ritula
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GMATPREP:Permutaion & combination [#permalink] GMATPREP:Permutaion & combination   29 Jan 2009, 04:18
Pls explain ur answers



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Re: GMATPREP:Permutaion & combination [#permalink] GMATPREP:Permutaion & combination   29 Jan 2009, 05:30
It will be 26 + (26*26) + (26*26*26)
= 18278
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Re: GMATPREP:Permutaion & combination [#permalink] GMATPREP:Permutaion & combination   29 Jan 2009, 08:30
1
Kudos
scthakur wrote:
It will be 26 + (26*26) + (26*26*26)
= 18278


Same approach.

just my 2 cents.. no need to calculate/multiple..
26 + (26*26) + (26*26*26) --> all these end with unit digit 6.
SUM OF THESE THREE NUMBERS must be NUMBR with unit digit 8
only one option available.
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Re: GMATPREP:Permutaion & combination [#permalink] GMATPREP:Permutaion & combination   29 Jan 2009, 10:33
+1 for this shortcut.
x2suresh wrote:
scthakur wrote:
It will be 26 + (26*26) + (26*26*26)
= 18278


Same approach.

just my 2 cents.. we no need to calculate/multiple..
26 + (26*26) + (26*26*26) --> all these end with unit digit 6.
so sum's last digit must be 8 only one option available.
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Re: GMATPREP:Permutaion & combination [#permalink] GMATPREP:Permutaion & combination   01 Feb 2009, 07:00
So..one thing to note here...may be people already know.

Permutation formula nPr = n! / (n-r)! doesnt consider repetitions :)



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01 Feb 2009, 07:00
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