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What is the mean number of defective pens in a box of pens? The probab

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Director
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What is the mean number of defective pens in a box of pens? The probab [#permalink]

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New post 04 Aug 2010, 15:17
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Question Stats:

42% (01:18) correct 58% (01:21) wrong based on 24 sessions

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What is the mean number of defective pens in a box of pens? The probability that there is exactly 1 defective pen in a box is 1 percent

(1) The probability that all the pens in the box are not defective is 96%
(2) The probability that there is more than 1 defective pen in the box is 3%
[Reveal] Spoiler: OA

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Director
Director
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Status: Impossible is not a fact. It's an opinion. It's a dare. Impossible is nothing.
Affiliations: University of Chicago Booth School of Business
Joined: 26 Nov 2009
Posts: 956

Kudos [?]: 902 [0], given: 36

Location: Singapore
Concentration: General Management, Finance
Schools: Chicago Booth - Class of 2015
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Re: What is the mean number of defective pens in a box of pens? The probab [#permalink]

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New post 05 Aug 2010, 00:09
The OA is E :shock:

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Re: What is the mean number of defective pens in a box of pens? The probab [#permalink]

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New post 05 Aug 2010, 07:06
The expected value of the number of defective pens is equal to the sum of each possible outcome times the probability of that outcome occuring. In other words, we have

0 * probability of no defective pens + 1 * probability of 1 defective pen + 2 * probability of 2 defective pens + ...

We have data for the first two terms in the sum, but we don't have the number of remaining terms (we don't know how many pens are in the box), hence we cannot compute the expectation (a.k.a. mean). We could write a formula for the expectation in terms of the number of pens in the box, but we cannot compute the actual value.

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Re: What is the mean number of defective pens in a box of pens? The probab [#permalink]

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New post 10 Oct 2010, 16:30
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1) says 96% of the boxes are good. 4% of the boxes have defective pen(s). we dont have the actual number of def pens and total num of pens or boxes to find out the mean

2) says 3% have more than 1 def pen and from the q, 1% have 1 def pen. same data as 1).

both lack further info
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Re: What is the mean number of defective pens in a box of pens? The probab [#permalink]

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New post 23 Sep 2017, 19:23
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Re: What is the mean number of defective pens in a box of pens? The probab   [#permalink] 23 Sep 2017, 19:23
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