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From |
Richard Goldstein <richgold@ix.netcom.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: probability question |

Date |
Wed, 28 Oct 2009 10:13:45 -0400 |

thank you! Brian P. Poi wrote: > On Wed, 28 Oct 2009, Richard Goldstein wrote: > >> >> 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? >> > > Perhaps beating Maarten to the punch, I immediately thought to do a > simulation, and I came up with 0.00048260, right in line with Al > Feiveson's analytic solution. > > ---------------------------------------- > mata: > > rseed(1) > tries = 10000000 > totaln = 0 > for(i=1; i<=tries; ++i) { > > // rain has 7 ones > rain = J(120, 1, 0) > rain[1..7] = J(7,1,1) > > // hat has 4 ones > hat = J(120, 1, 0) > hat[1..4] = J(4,1,1) > > // shuffle each one > _jumble(rain) > _jumble(hat) > > // if there's a match, hat+rain==2 > both = rain + hat > matches = sum(both:==2) > // we want to know if there were three matches > if (matches == 3) { > totaln = totaln + 1 > } > if (mod(i, 1000) == 0) { > printf(".") > } > } > > > printf("\n\nProbability is about %10.8f\n", totaln/tries) > > end > ---------------------------------------- > > > -- Brian Poi > -- bpoi@stata.com * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: probability question***From:*Richard Goldstein <richgold@ix.netcom.com>

**Re: st: probability question***From:*"Brian P. Poi" <bpoi@stata.com>

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