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# Probability

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Intern
Joined: 22 Apr 2008
Posts: 15

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01 Aug 2008, 15:25
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Hi,

If 2 people are to create a user name made up of 7 characters (can use any of the 26 alphabets or the 10 digits, repeats allowed). What is the probability that these 2 people will create the exact same user name (assuming that these people don't know each other at all)?

Thanks!
Director
Joined: 27 May 2008
Posts: 540

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01 Aug 2008, 16:35
hl1711 wrote:
Hi,

If 2 people are to create a user name made up of 7 characters (can use any of the 26 alphabets or the 10 digits, repeats allowed). What is the probability that these 2 people will create the exact same user name (assuming that these people don't know each other at all)?

Thanks!

since repeates are allowed, there are 36^7 different usernames possible ... lets call them 1,2,3.......36^7
our 2 people are A and B....

Probablity that A takes 1 and B also takes 1 = 1/36^7 * 1/36^7
Probability that A takes 2 and B also takes 2 = 1/36^7 * 1/36^7
similarly other .... from 1 to 36^7

final probability = 36^7 * (1/36^7 * 1/36^7) = 1/36^7
Intern
Joined: 22 Apr 2008
Posts: 15

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01 Aug 2008, 21:25
durgesh79 wrote:
hl1711 wrote:
Hi,

If 2 people are to create a user name made up of 7 characters (can use any of the 26 alphabets or the 10 digits, repeats allowed). What is the probability that these 2 people will create the exact same user name (assuming that these people don't know each other at all)?

Thanks!

since repeates are allowed, there are 36^7 different usernames possible ... lets call them 1,2,3.......36^7
our 2 people are A and B....

Probablity that A takes 1 and B also takes 1 = 1/36^7 * 1/36^7
Probability that A takes 2 and B also takes 2 = 1/36^7 * 1/36^7
similarly other .... from 1 to 36^7

final probability = 36^7 * (1/36^7 * 1/36^7) = 1/36^7

You folks are amazing! Thanks so much.
Re: Probability   [#permalink] 01 Aug 2008, 21:25
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# Probability

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