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RAIN

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Manager
Joined: 20 May 2008
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RAIN [#permalink]  28 Jan 2009, 22:54
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..
SVP
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Re: RAIN [#permalink]  29 Jan 2009, 02:13
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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Re: RAIN [#permalink]  29 Jan 2009, 08:11
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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Re: RAIN [#permalink]  29 Jan 2009, 08:23
agree with GMATTIGER approach.
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Manager
Joined: 01 May 2008
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Re: RAIN [#permalink]  08 Feb 2009, 15:43
GMATTIGER, can u explain why u multiplied 6C3?
Thanks a lot
Re: RAIN   [#permalink] 08 Feb 2009, 15:43
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