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# Rainy day

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Intern
Joined: 09 Apr 2003
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13 Apr 2003, 16:18
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

I saw this question on the GMAT club website. Not sure whether I solved this right.

The probability that it will rain in NYC on any given day in July is 30%. what is the probability that it will rain on exactly 3 days from July 5 to July 10 ?

6C3 * (0.3*0.3*0.3*0.7*0.7*0.7) = 0.18522

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Manager
Joined: 24 Jun 2003
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Location: India

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26 Jun 2003, 08:56
ABNY

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SVP
Joined: 03 Feb 2003
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27 Jun 2003, 01:05
The initial solution was mine
BB posted this question

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Director
Joined: 03 Jul 2003
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06 Jul 2003, 20:19
Why should the answer be multiplied with 6C3?
Why not just (0.3*0.3*0.3*0.7*0.7*0.7) ?

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SVP
Joined: 03 Feb 2003
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06 Jul 2003, 23:19
The rainy days go in different order. We have to count all the combinations.

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Manager
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07 Jul 2003, 07:14
P(rainy day ) = 0.3
P(Shiny day ) = 1 - 0.3 = 0.7

If you apply Binomial Probablity Distribution, we get
P(of getting rain on 3 days out of 6 days) = 6C3 X (0.3)3 X (0.7)3

( where (0.3)3 = 0.3X0.3X0.3 )
_________________

Brainless

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07 Jul 2003, 07:14
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