Being really bad in Statistics, need some help here. The problem is : We draw a sample of 20 laptops from a population of 1000 Laptops (serial numbers from 9000-9999). a. What distribution should i use for the serial number selected? b. What is the probability a randomly selected will be one of the last 200 to be produced. c. What is the probability the first 2 are from the last 100 to be manufactured. ** The purpose of sampling is to check the quality of the laptops, thus there are two outcomes: faulty or not-faulty.

  • $\begingroup$ What distributions do you already know of? $\endgroup$ Jun 4, 2014 at 8:22
  • $\begingroup$ I am a returning student to uni, thus i can't be sure what i'm supposed to know. I believe because the sample is small, i should go with binomial. b. the probability is 0.2 c. the prob is 0.1 * 0.1. Is it that simple? or im missing something there? $\endgroup$ Jun 4, 2014 at 8:29
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    $\begingroup$ 'What distribution should i use for the serial number selected?' - do you mean for the serial numbers of the sampled laptops? $\endgroup$
    – Alex
    Jun 4, 2014 at 8:38
  • $\begingroup$ You should use the hypergeometric distribution. $\endgroup$
    – user64494
    Jun 4, 2014 at 8:38
  • $\begingroup$ I have edited my question. I assume that since we want to check the faulty laptops, the question refers to that fact given the sample. Hypergeometric was my initial thought, but the sample is small (<5%) $\endgroup$ Jun 4, 2014 at 8:50

1 Answer 1


Hint: I think we are supposed to assume all the serial numbers are equally likely to be selected. Suppose you select just one serial number. Then it is a number from 9000 to 9999, all of which are equally likely. Can you give that distribution a name?

  • $\begingroup$ Oh, it is just a uniform distribution, right? $\endgroup$ Jun 4, 2014 at 19:44
  • $\begingroup$ Thank you so much for your help, seems like i really need to refresh the basics in Statistics. $\endgroup$ Jun 5, 2014 at 2:28

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