Probability

There is a big line of people waiting outside a bar for buying drinks. The owner comes out and says that the first person to have a birthday same as someone standing before him in the line gets a free drink.

You're standing at position 25 in the line. What is the probability that you get the free drink?

Note: no fancy probability tricks required. (Favorable cases)/(Total cases) will work.

12 comments:

  1. RohinDecember 24, 2011 at 9:43 PM

    {(364/365)^24}*(1/365) ?

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  2. AnujDecember 25, 2011 at 5:14 PM

    that's not correct.

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  3. ShivankerDecember 25, 2011 at 8:28 PM

    come on people!

    ReplyDelete
  4. Pulkit MendirattaDecember 26, 2011 at 12:01 AM

    a quick guess - (363/364)^23*(1/364)

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  5. RohinDecember 26, 2011 at 3:48 PM

    (133224/133,225)^24*(1/365)^2?

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  6. PrateekDecember 26, 2011 at 5:31 PM

    {(364/365)^23}*{(1/365)^2}

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  7. AnujDecember 26, 2011 at 6:12 PM

    The answer is:

    (365,24)*24!*24
    ---------------
    365^24

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  8. AnujDecember 26, 2011 at 6:22 PM

    (n,r) denotes nCr

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  9. UnknownDecember 26, 2011 at 8:59 PM

    @Anuj bhaiya... i think the power of 365 should be 25 in the denominator.

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  10. AnujDecember 26, 2011 at 10:06 PM

    that's right.

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  11. Pulkit MendirattaDecember 26, 2011 at 10:55 PM

    Oh :P Didnt read 'someone' in 'the first person to have a birthday same as someone standing before him in the line'

    ReplyDelete
  12. AnujDecember 27, 2011 at 9:50 PM

    Has some 'JEE aspirant' been able to solve it? So far its me, Shivanker and Dhwanit (and the problems are not meant for us).

    ReplyDelete

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