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Math Help - Probality of defective bolts

  1. #1
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    Probality of defective bolts

    Sample 200 bolts
    24 bolts ae defective for poor workmanship
    34 bolts are defective due to size too big
    158 bolts meet specification
    if a bolt is selected what is s the probability that it wilill be defective for 1 too large. large
    2.poor workmanship but not b0th

    Am I on the right track

    P = 24 +34/200

    P(24/34) = P(24 * 154)/200


    I am quite sure how to approach this problem
    Last edited by masimini25; February 2nd 2010 at 07:56 PM. Reason: spelling
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  2. #2
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    I'm not entirely clear on what your question is, but I think the key is that there are some bolts which are both oversize and have poor workmanship.

    200-158 = 42 bolts are defective in some way, but 24+34 = 58 - more than 42. You need to figure out exactly how many bolts are in each category - that is, how many are too large, how many are poor workmanship, and how many are both. It might help to draw a Venn diagram.
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  3. #3
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    Sample 200 bolts
    24 bolts ae defective for poor workmanship
    34 bolts are defective due to size too big
    158 bolts meet specification
    if a bolt is selected what is s the probability that it wilill be defective for 1 too large. large
    2.poor workmanship but not b0th

    Am I on the right track

    P = 24 +34/200

    It says draw a venn diagram
    The question is if only 1bolt is selected what is the probability tha it will be found defective for only one reason( ie it is either too large or has poor workmanship, but not both. Then Draw avenn diargam
    Thank you I am still haivng ahrd time
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  4. #4
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    Ok, I see. So yes, you're on the right track, but your problem is that (24 + 34) also includes all the bolts that are defective for BOTH reasons. You need to figure out how many this is.

    So, your answer will be the total number of broken bolts (24+34) MINUS the number of bolts that have BOTH problems, all over 200.

    To figure out how many bolts have both problems, consider this: how many bolts are broken? (entire sample MINUS working bolts). What is 24 + 34? What's the difference?

    Like I said, it might be useful to draw the Venn diagram first.
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