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May 13th, 2008, 05:07 PM   #1
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Tricky question for me

Hi, I need some help with the following question.

The production of a certain machine has a 5% of producing a faulty machine, there is a 0.91 chance that the faulty machines will be discarded and a 0.03 chance that a working machine will be discarded. How many of the machines in the discarded pile are faulty? Answer in percent.

I could really use some help with this one. Thanks.
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May 14th, 2008, 02:26 AM   #2
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Here's a way to do this without using any statistics or probability. Say you have 2000 machines. Now, 5% of them are faulty, or in other words 100 machines. This gives us 1900 machines to be working. Also, 91% of the faulty ones will be discarded - 91 machines. As for the working ones, 3% will be discarded - 57. So, we have the total number of discarded ones - 57+91=148 and hence the percentage of the faulty machines in the discarded pile is 91/148 ≈ 61.48%.
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May 15th, 2008, 05:24 AM   #3
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Ahh I see, smart.

Thanks!
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