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May 13th, 2008, 05:07 PM  #1 
Newbie Joined: May 2008 Posts: 4 Thanks: 0  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. 
May 14th, 2008, 02:26 AM  #2 
Senior Member Joined: May 2007 Posts: 402 Thanks: 0 
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%.

May 15th, 2008, 05:24 AM  #3 
Newbie Joined: May 2008 Posts: 4 Thanks: 0 
Ahh I see, smart. Thanks! 

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