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Math Help - mean and standard deviation + check!

  1. #1
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    mean and standard deviation + check!

    1) The mean and standard deviation of a set of data are two measurements that describe the data. A certain student has written 8 out 10 exams, which are equally weighed. The student misses the 9th exam and receives a score of 0. However, for the last exam, the student studied an incredible amount and scored 100% compare the mean and standard deviation after 8 unit test and after 10 unit test.
    My answer:
    Both the mean and standard deviation are 50.

    2) The following data in the sodium content (in milligrams) of 20 beef hotdogs:
    495,477,425,322,482,587,370,322,479,375,330,300,38 6,401, 645, 440,317,319,298, 253
    Determine the mean and standard deviation of the data:
    My answer:
    Mean: 401.15
    Standard deviation: 99.84


    7) What is the mean and standard deviation?
    Value:
    4.8
    5.2
    5.4
    5.9
    6.5
    6.6
    Frequency:
    25
    21
    23
    17
    24
    25

    My answer:
    Mean: 5.74
    Standard deviation: 0.69

    Can someone please check thanks!!!!!
    Last edited by bobbluecow; June 1st 2007 at 10:39 AM. Reason: Can someone please check thanks!!!!!
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  2. #2
    Newbie
    Joined
    Nov 2006
    Posts
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    I know 2 are right but not sure about the first one....

    To be honest I can tell you that 2 and 7 are right: but I am not sure about question one maybe someone else can answer well good luck in your studies I am doing statistics and man is it ever confusing but mean and standard deviation are straight foward. well good luck!

    2) The following data in the sodium content (in milligrams) of 20 beef hotdogs:
    495,477,425,322,482,587,370,322,479,375,330,300,38 6,401, 645, 440,317,319,298, 253
    Determine the mean and standard deviation of the data:
    My answer:
    Mean: 401.15
    Standard deviation: 99.84

    correct good job


    7) What is the mean and standard deviation?
    Value:
    4.8
    5.2
    5.4
    5.9
    6.5
    6.6
    Frequency:
    25
    21
    23
    17
    24
    25

    My answer:
    Mean: 5.74
    Standard deviation: 0.69 correct good job
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  3. #3
    Grand Panjandrum
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    someplace
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    Thanks
    4
    Quote Originally Posted by bobbluecow View Post
    1) The mean and standard deviation of a set of data are two measurements that describe the data. A certain student has written 8 out 10 exams, which are equally weighed. The student misses the 9th exam and receives a score of 0. However, for the last exam, the student studied an incredible amount and scored 100% compare the mean and standard deviation after 8 unit test and after 10 unit test.
    My answer:
    Both the mean and standard deviation are 50.
    Let the sum of the marks on the first 8 exams be S_8 and the
    sum of the squares of the marks be SS_8. Then the mean
    of the first eight exams is:

    <br />
\mu_8 = S_8/8<br />

    and the standard deviation is:

    <br />
\sigma_8 = \sqrt{(SS_8 - (S_8)^2)/8}<br />

    Now the sum of all the exams S_{10}=S_8 + 100, and the sum of squares
    SS_{10}=SS_8 + 10000. Then the final mean is:

    <br />
\mu_{10} = (S_8+100)/10 = (8\mu_8 + 100)/10<br />

    and the standard deviation is:

    <br />
\sigma_{10} = \sqrt{(SS_{10} - (S_{10})^2)/10}<br />

    Now this last needs to be rewitten in terms of \mu_8 and \sigma_8, which
    is tedious but routine.

    RonL
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