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# How many randomly assembled people do u need to have a

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Manager
Joined: 16 Oct 2008
Posts: 54
How many randomly assembled people do u need to have a [#permalink]

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28 Oct 2008, 05:50
3.How many randomly assembled people do u need to have a better than 50% prob. that at least 1 of them was born in a leap year?

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Director
Joined: 14 Aug 2007
Posts: 695

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28 Oct 2008, 07:01
Natasha0123 wrote:
3.How many randomly assembled people do u need to have a better than 50% prob. that at least 1 of them was born in a leap year?

Heck, this took a long time..I don't think this question will appear in GMAT though.
Can you also please provide options when you post questions?

Leap year occurs once every 4 years, so probability of any random person to be born in leap year is 1/4.
I think minimum 3 people will be needed, but am not sure unless options are provided.
Manager
Joined: 16 Oct 2008
Posts: 54

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28 Oct 2008, 07:04
Thanks a lot Really, but there's no option provide..

Here' the solution, really confuse

Prob. of a randomly selected person to have NOT been born in a leap yr = 3/4
Take 2 people, probability that none of them was born in a leap = 3/4*3/4 = 9/16. The probability at least one born in leap = 1- 9/16 = 7/16 < 0.5
Take 3 people, probability that none born in leap year = 3/4*3/4*3/4 = 27/64.
The probability that at least one born = 1 - 27/64 = 37/64 > 0.5

Thus min 3 people are needed.
VP
Joined: 05 Jul 2008
Posts: 1333

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28 Oct 2008, 13:01
Natasha0123 wrote:
Thanks a lot Really, but there's no option provide..

Here' the solution, really confuse

Prob. of a randomly selected person to have NOT been born in a leap yr = 3/4
Take 2 people, probability that none of them was born in a leap = 3/4*3/4 = 9/16. The probability at least one born in leap = 1- 9/16 = 7/16 0.5

Thus min 3 people are needed.

The problem makes an assumption that all people are born in the same century??? I was stuck on that for a while.

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
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# How many randomly assembled people do u need to have a

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