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January 16th, 2011, 04:23 AM  #1 
Newbie Joined: Jan 2011 Posts: 17 Thanks: 0  Stats question [thanks!]
Hey so I have a stats question I need a bit of help on...here it is : A store sells HD recorders, assuming that the weekly demand for recorders is a Poisson variable with a mean of 3, find the probability that the store sells more than 20 in a month (4 week period). Now I've tried this question by trying to find the mean amount sold within a month which is 12 (3 x 4) and then used a poisson dist. to find an answer of 0.116, can anyone tell me if this is right or the wrong way of doing it. Also, another part to the same question: Find the minimum number that should be in stock at the beginning of the month so that the store can be at least 95% sure of being able to meet demands of that month. I think you require logs to solve that problem, but I'm not too sure, so I was wondering if anyone could help me find a solution to it. Thanks in advance! 
January 16th, 2011, 07:51 AM  #2 
Newbie Joined: Jan 2011 Posts: 17 Thanks: 0  Re: Stats question [thanks!]
Anyone? 
January 18th, 2011, 10:11 AM  #3  
Newbie Joined: Jan 2011 Posts: 1 Thanks: 0  Re: Stats question [thanks!]
For the first part, you are correct! I used Mathematica 8 to check the answer: Quote:
The second part is asking how many items (x) you need to have in stock, so that you will meet the demand (y) with at least 95% probability. One way to go about is to adding all the possible outcomes until you have a probability greater than 0.95. Quote: Alternatively, I used Mathematica to calculate: Quote:
 

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