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    June 2010, S2, edexcel
    http://www.edexcel.com/migrationdocu...e_20100609.pdf

    http://www.edexcel.com/migrationdocu...c_20100714.pdf

    Question 6.
    A company claims that a quarter of the bolts sent to them are faulty. To test this claim the number of faulty bolts in a random sample of 50 is recorded.
    The number of faulty bolts was 8
    Comment on the company’s claim in the light of this value. Justify your answer.



    I thought that all you have shown (by hypothesis testing in the earlier parts of the question) is that there is not significant evidence (to 5%) to reject the companies claim, and that you have in no way shown the claim to be correct.

    However the mark scheme says "There is evidence that the probability of a faulty bolt is 0.25 or the company’s claim is correct."
    Which is right?
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    (Original post by Nick_)
    I thought that all you have shown (by hypothesis testing in the earlier parts of the question) is that there is not significant evidence (to 5%) to reject the companies claim, and that you have in no way shown the claim to be correct.

    However the mark scheme says "There is evidence that the probability of a faulty bolt is 0.25 or the company’s claim is correct."
    Which is right?
    There is no evidence to reject the company's claim (the null hypothesis), and therefore we accept it.

    To say that it is "correct" however is a big step, and one I wouldn't make.

    We could state that p(faulty bolt) = 0.2, and by the same test results, we would accept that. They can't both be correct.

    So, markscheme is wrong, IMHO.

    Your original interpretation is the correct one.
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    (Original post by Nick_)
    June 2010, S2, edexcel
    http://www.edexcel.com/migrationdocu...e_20100609.pdf

    http://www.edexcel.com/migrationdocu...c_20100714.pdf

    Question 6.
    A company claims that a quarter of the bolts sent to them are faulty. To test this claim the number of faulty bolts in a random sample of 50 is recorded.
    The number of faulty bolts was 8
    Comment on the company’s claim in the light of this value. Justify your answer.



    I thought that all you have shown (by hypothesis testing in the earlier parts of the question) is that there is not significant evidence (to 5%) to reject the companies claim, and that you have in no way shown the claim to be correct.

    However the mark scheme says "There is evidence that the probability of a faulty bolt is 0.25 or the company’s claim is correct."
    Which is right?
    Well by reading the question you should know that this a binomial distribution.
    X~B (50,0.25)
    H0: P= 0.25 ; H1: P<0.25
     => P(X<(equal)5) =0.0070<0.01 => reject H0
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    (Original post by dan94adibi)
    Well by reading the question you should know that this a binomial distribution.
    X~B (50,0.25)
    H0: P= 0.25 ; H1: P<0.25
     => P(X<(equal)5) =0.0070<0.01 => reject H0
    thank you, but it was actually part d i was looking at
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    Sorry about that.

    Well you are looking for P(X<(equal)8) = 0.0916 > 0.025

    Therefore there is not enough evidence to reject H0 hence the company is correct.


    Correct me if I'm wrong.
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    (Original post by dan94adibi)
    Sorry about that.

    Well you are looking for P(X<(equal)8) = 0.0916 > 0.025

    Therefore there is not enough evidence to reject H0 hence the company is correct.


    Correct me if I'm wrong.
    Don't worry, my point was simply that the test does not say that the company is right, only that it is not shown to be wrong.
 
 
 
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