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January 30th, 2012, 09:20 AM  #1 
Newbie Joined: Jan 2012 Posts: 1 Thanks: 0  Statistics (Normal distribution) help.
Problem: It may be assumed that dates of birth in a large population are distributed throughout the year so that the probability of a randomly chosen person's date of birth in any particular month may be taken as 1/12. a) Find the probability that of 6 people chosen at random exactly two will have birthdays in January. b) Find the probability that of 8 people chosen at random at least one will have birthdays in January. c) N people are chosen at random. Find the least value of N so that the probability that at least one will have a birthday in January exceeds 0.9 d) Find the probability that of 100 people chosen at random, at least 40 will have birthdays in May, June or August. Ans: (a) 0.07355 (b) 0.5015 (c) 27 
January 31st, 2012, 08:25 PM  #2 
Senior Member Joined: Apr 2011 From: USA Posts: 782 Thanks: 1  Re: Statistics (Normal distribution) help.
These are all correct. (c) was interesting  I've never worked into one backwards before. Of course, I could have just tested your answer against 26 & 28, but it wouldn't have been any fun if I hadn't tried it myself. What have you tried on (d)? I assume they want a normal approximation of a binomial? Is that something you've been learning? 

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