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GMAT Prep : Combination ?

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by narik11 » Sun Oct 03, 2010 11:31 am
Skywalker wrote:How to solve this one ....
OA == option E . Thanks

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It says the letters can be repeated:
It also says same letters used in different order constitute to different code, So AB is different form BA
So 26+26^2+26^3=18278
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by Rahul@gurome » Sun Oct 03, 2010 5:44 pm
1 letter code can be selected in 26 ways
2 letter code can be selected in 26 ^2 = 676 ways
3 letter code can be selected in 26 ^3 = 17,576 ways
Therefore, required number of codes = 26 + 676 + 17,576 = 18,278

[spoiler]The correct answer is (E).[/spoiler]
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by goyalsau » Mon Oct 04, 2010 2:39 am
narik11 wrote:
Skywalker wrote:How to solve this one ....
OA == option E . Thanks

Image
It says the letters can be repeated:
It also says same letters used in different order constitute to different code, So AB is different form BA
So 26+26^2+26^3=18278
Can you please explain the logic behind it,
why its not 26^3...
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