## Probability of Defective Items

Standard deviation, mean, variance, z-scores, t-tests, etc.
justin_pscl
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Joined: Sat Jul 17, 2010 6:10 pm
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### Probability of Defective Items

Hello, I needed some help with a problem. Okay, here it goes.

A manufacturer makes two models of an item: model I, which accounts for 80% of unit sales, and model II, which accounts for 20% of unit sales. Because of defects, the manufacturer has to replace (or exchange) 10% of its model I and 18% of its model II. If a model is selected at random, find the probability that it will be defective.

Now there are two models. What I did was I added the 80% and 20% and I got 100%. The next thing I did was I added the 10% and the 18% to get 28%. After that I kind of lost myself. Looking forward to answer. Oh and the answer in the back of the back says its 0.116. Thanks.

maggiemagnet
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Joined: Mon Dec 08, 2008 12:32 am
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### Re: Probability of Defective Items

What is the probability that the item you've picked is Model 1? Assuming that you've picked a Model 1, what is the probability that it is defective? Then what is the probability that you've picked a defective unit of Model 1?

What is the probability that the item you've picked is Model 2? Assuming that you've picked a Model 2, what is the probability that it is defective? Then what is the probability that you've picked a defective unit of Model 2?