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# RAIN

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Manager
Joined: 20 May 2008
Posts: 55

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28 Jan 2009, 23:54
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

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?

please give full explanation with reasons..

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SVP
Joined: 17 Jun 2008
Posts: 1530

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29 Jan 2009, 03:13
Total number of days between the two days (inclusive) = 6.

Probability of choosing 3 days on which it rains = 3/6 = 1/2
Probability that it rains on exactly these three days = (1/2)*30% = 15%

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SVP
Joined: 29 Aug 2007
Posts: 2470

Kudos [?]: 867 [0], given: 19

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29 Jan 2009, 09:11
LoyalWater wrote:
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?

please give full explanation with reasons..

= 6C3 (0.3)^3 (1-0.3)^(6-3)
= 20 (0.3^3)(0.7^3)
= 18.52%
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SVP
Joined: 07 Nov 2007
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29 Jan 2009, 09:23
agree with GMATTIGER approach.
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Smiling wins more friends than frowning

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Manager
Joined: 01 May 2008
Posts: 110

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Location: São Paulo

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08 Feb 2009, 16:43
GMATTIGER, can u explain why u multiplied 6C3?
Thanks a lot

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Re: RAIN   [#permalink] 08 Feb 2009, 16:43
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# RAIN

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