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Math Help - Statistics Homework Help

  1. #1
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    Statistics Homework Help

    Question:
    Julie took five test; her scores are as follows:
    IQ 110
    SAT Math 605
    SAT Verbal 590
    math Ach. z = 1.3
    Science Ach. PR = 84

    They want all the z scores. How do you find the Z score for PR?
    The Standard Deviation is 15. Mean 100.
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  2. #2
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    Quote Originally Posted by CavalryScout View Post
    Question:
    Julie took five test; her scores are as follows:
    IQ 110
    SAT Math 605
    SAT Verbal 590
    math Ach. z = 1.3
    Science Ach. PR = 84

    They want all the z scores. How do you find the Z score for PR?
    The Standard Deviation is 15. Mean 100.
    z = \frac{X - \mu}{\sigma}, where in this case X = PR = 84.
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    Question Stat help

    Can you explain what the symbols stand for?
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    Quote Originally Posted by CavalryScout View Post
    Can you explain what the symbols stand for?
    \mu = mean.
    \sigma = standard deviation.

    Maybe you're more comfortable with

    <br />
z = \frac{X - \bar{X}}{s.d.}<br />
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  5. #5
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    PR is percentile and you need a raw score to use that formula according to this formula sheet. Its so confusing.
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  6. #6
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    Quote Originally Posted by CavalryScout View Post
    PR is percentile and you need a raw score to use that formula according to this formula sheet. Its so confusing.
    PR is a statistic that presumably follows a normal distribution. You have a value for PR, a mean for PR and a standard deviation for PR. You put those into the formula:

    z = \frac{PR - \bar{PR}}{s.d.} = \frac{84 - 100}{15} = -\frac{16}{15}.

    But for my money, it doesn't make sense to say PR has a mean of 100 ..... I would've thought the mean of a percentile was 50 by definition ......

    In which case, z = \frac{PR - \bar{PR}}{s.d.} = \frac{84 - 50}{15} = \frac{34}{15} = 2.27, correct to 2 dp.

    Maybe someone else will jump in and offer their 2 cents worth ....
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