Tuesday, August 18, 2009

Permutation and Combination - Step by Step approach - 3

Hi,

In continuation to approach in P&C here are some more questions to continue with

1. In how many ways can you post 10 letters in 4 letterboxes?

2.Four friends go to a city in which there are 10 hotels

a.In how many ways can they stay?
b.In how many ways can they stay if no two friends stay together?
c.In how many ways can they stay if atleast two friends stay together?

Post your answers to the above questions. OA will be posted soon.

Thanks,
Quant-Master
Posted by GMAT at 12:23 AM

1 comment:

  1. GMATAugust 20, 2009 at 12:20 AM

    Approach to question 1:

    You have 10 letters and 4 letterboxes. Take letter 1 you can post that in either box 1 or 2 or 3 or 4 (4 ways), Letter 2 in the similar way can be posted in 4 ways, all the letters till letter 10 can be posted in 4 ways.

    Now what do we need to do add all the 4s or multiply all the 4s?

    Before you see the answer think by yourself

    I guess you guys must have got it right.

    Since we are posting letter 1 AND letter 2 AND letter 3...AND letter 10 we need to multiply. If any of you is not sure than have a look at my previous post on permutation and combination.

    hence 4*4*....*4 = 4^10 ways

    Now here is the funda

    Number of ways of arranging r distinct items in n distinct things, where each things can be used any number of times is n^r

    Try and post the answers for 2nd question and let me know if you have any queries

    Thanks,
    Quant-Master

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