Probability of Being Struck by Lightning
Date: Wed, 23 Aug 1995 15:19:22 -0400 From: Pat Vennebush Subject: Probability problem Dear Dr. Math, OF the 3.4 million secretaries in the US, 39,000 are male. While all 3.4 million secretaries were at the annual secretaries' day picnic, a vicious storm began. Lightning headed directly for the secretaries. Given that males are eight times as likely to be hit by lightning as females, what is the probability that one of the male secretaries will be struck? (Of course, this problem assumes that the lightning will indeed hit one of the attendees, and not a tall tree or a metal flagpole. Also, let me say that both of these facts are true: only 39,000 of the 3,400,000 secretaries in the US are male--or so Business Week says--and an article several years ago in _Men's Health_ titled "The Gender Gap" stated that men are eight times as likely to be hit by lightning.) Anyway, looking forward to hearing from ya, doc. Sincerely, Patrick Vennebush MATHCOUNTS Curriculum Coordinator
Date: 8/23/95 at 15:35:10 From: Doctor Ken Subject: Re: Probability problem Hello there! Well, I just got your question a second ago, and I just can't resist replying right away, because as a man, I want to figure out the answer! The way you can use the "eight times as likely" information is to say that for every man at the convention, there are seven additional "virtual" men standing there beside them to proxy for them in case of lightning. So the effective number of male secretaries at the convention is eight times the actual number, i.e. 39,000 * 8 = 312,000 male secretatries. This also changes the total number of secretaries at the convention, so we can add the number of female secretaries to this new number, and get 3,361,000 + 312,000 = 3,673,000 which is our new total number of secretaries. Now we just divide: 312,000/3,673,000 = .0849, the probability that a man will be struck. Compare that with the value you'd get if men were equally likely to get struck: 39,000/3,400,000 = .0115, which is more than one-eighth of the other probability: the probability went up less than eight-fold with the additional information from Men's Health. -Doctor Ken, The Geometry Forum
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