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Math Help - [SOLVED] Average credit score

  1. #1
    Famas
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    [SOLVED] Average credit score

    At a bank, average credit score of a 35 yr old is normally distributed with a mean of 600 and std dev of 100.

    a. score for top 5%
    b. 75% of applicants will have at least what score?
    c. Between what two credit scores will 80% of the applicants fall if the applicants are symmetrically distributed?

    Please help thanks!

    doesn't this problem involve finding the z score? but 5-600/100 = a number outside the chart
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  2. #2
    Flow Master
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    Quote Originally Posted by Famas View Post
    At a bank, average credit score of a 35 yr old is normally distributed with a mean of 600 and std dev of 100.

    a. score for top 5%
    b. 75% of applicants will have at least what score?
    c. Between what two credit scores will 80% of the applicants fall if the applicants are symmetrically distributed?

    Please help thanks!

    doesn't this problem involve finding the z score? but 5-600/100 = a number outside the chart
    a. Z = \frac{X - 600}{100}

    You want the value of \alpha such that \Pr(X > \alpha) = 0.05.

    Note that Pr(Z > 1.64485) = 0.05.

    Therefore 1.64485 = \frac{\alpha - 600}{100} \Rightarrow \alpha = ....

    b. Do similarly to a.

    c. You want the value of \beta such that \Pr(X > \beta) = 0.1. Draw a simple curve and you'll see this. Now do similarly to a.

    The lower and upper credit scores are then 600 - (\beta - 600) = 1200 - \beta\, and \, \beta.
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