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Re: st: probability question


From   Richard Goldstein <richgold@ix.netcom.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: probability question
Date   Wed, 28 Oct 2009 09:36:55 -0400

thank you!

Jeph Herrin wrote:
> 
> Prob(rain) = 7/120
> Prob(no rain) = 113/120
> 
> X=days it rains on hat
> 
> Prob(X=3)=c(4,3)*(7/120)^3*(113/120)^1
>          =4*0.0001985*0.94
>          =0.0007477
> 
> 
> not much chance!
> 
> 
> Richard Goldstein wrote:
>> it's been a long time since I thought about questions like this, but, as
>> a lead-in to a study, a client has asked the following question which he
>> thinks he understands and says is related to where he wants to go:
>>
>> during a consecutive period of 120 days, if it rains on 7 days and my
>> client wears a hat on 4 days (these are independent of any knowledge of
>> the weather), what is the probability that it will rain on 3 of the days
>> on which he is wearing a hat?
>>
>> my client swears that this is not a homework problem for him or his wife
>> or one of their kids!
>>
>> Rich
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