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Probability Question

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Probability Question [#permalink] New post 19 Apr 2014, 05:40
Hi Guys

I need some help with a question below:
Three workers produce a certain part at the same rate .Joe averages 2 defective parts per hundred.Mary averages 5 defective parts per hundred.Harold averages 8 defective parts per hundred.The defective parts are identified by quality control and set aside in a rework pile.

How many defective parts do you expect there to be out of 1000 parts produced?

What is the probability that a randomly selected part in the rework pile was produced by Mary?
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Re: Probability Question [#permalink] New post 26 Apr 2014, 01:57
I think that its very tough for me. I also think that I also required training for such questions.
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Re: Probability Question [#permalink] New post 30 Apr 2014, 10:09
Expert's post
Takalm wrote:
Hi Guys

I need some help with a question below:
Three workers produce a certain part at the same rate .Joe averages 2 defective parts per hundred.Mary averages 5 defective parts per hundred.Harold averages 8 defective parts per hundred.The defective parts are identified by quality control and set aside in a rework pile.

How many defective parts do you expect there to be out of 1000 parts produced?

What is the probability that a randomly selected part in the rework pile was produced by Mary?



Takalm,
Break this question down into pieces.
If they each work at the same rate, they will produce the same # of units. So out of the 1000, it's pretty much divided up as 333, 333, 333.

The # of defective parts in those 3 groups will vary. The first 333 will have a defect rate of 2%. The second set will have a defect rate of 5%. And the third set will have a defect rate of 8%.

So how many defects are produced? Add them up. 2% of 333 + 5% of 333 + 8% of 333.

Once you have the total # of defects....look at that out of the total 1000 (or 999) items that were produced. What's the defect rate overall?

Hint: it should be some average between the 2%, 5% and the 8%.
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Re: Probability Question [#permalink] New post 30 Apr 2014, 10:29
Takalm wrote:
Hi Guys

I need some help with a question below:
Three workers produce a certain part at the same rate .Joe averages 2 defective parts per hundred.Mary averages 5 defective parts per hundred.Harold averages 8 defective parts per hundred.The defective parts are identified by quality control and set aside in a rework pile.

How many defective parts do you expect there to be out of 1000 parts produced?

What is the probability that a randomly selected part in the rework pile was produced by Mary?


If they each produced 100 (for 300 total), how many defective parts are there?
Answer: 2+5+8 = 15.

Mary produced 5 of these 15.
So, if we randomly selected a part in this rework pile, the probability of it being Mary's is 5/15 = 1/3 = 33%

For every 300 parts produced, 15 are defective, as we figured out above.
So for every 100 parts produced, 5 are defective. (divided both sides by 3)

Then, for every 1000 parts produced, 50 are defective. (multiply both by 10).
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Re: Probability Question   [#permalink] 30 Apr 2014, 10:29
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