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Math Help - Find the Variance

  1. #1
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    Find the Variance

    So here is my question:

    Here for the r.v. Degree, 1 represents a leading role and 2 represents a secondary role. What is the variance of the r.v. Degree?

    Degree Females Males Sigmas
    1 7 3 10
    2 28 12 40
    Sigmas 35 15 50

    I do not understand how to get the variance from this. Any help on the procedure would be appreciated!
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  2. #2
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    Quote Originally Posted by Mistini View Post
    So here is my question:

    Here for the r.v. Degree, 1 represents a leading role and 2 represents a secondary role. What is the variance of the r.v. Degree?

    Degree Females Males Sigmas
    1 7 3 10
    2 28 12 40
    Sigmas 35 15 50

    I do not understand how to get the variance from this. Any help on the procedure would be appreciated!
    ...What?
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  3. #3
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    The numbers kinda scooted closer together, but for the top row it should read 7 females, 3 males and a total of 10 for for the leading role. Then the second role is 28 females and 12 males with a total of 40 for that row. I just have to find the variance of both rows. Instead of 1 and 2, you can replace them with Leading Role and Secondary Role if that helps. I just dont understand which numbers to use to find the variance.

    Maybe if I reword it?

    Leading Role 7females 3males
    Secondary 28females 12 males

    What is the variance among the roles?
    Last edited by Mistini; May 5th 2010 at 04:06 PM. Reason: to add more to the equation
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  4. #4
    Super Member Anonymous1's Avatar
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    Quote Originally Posted by Mistini View Post
    The numbers kinda scooted closer together, but for the top row it should read 7 females, 3 males and a total of 10 for for the leading role. Then the second role is 28 females and 12 males with a total of 40 for that row. I just have to find the variance of both rows. Instead of 1 and 2, you can replace them with Leading Role and Secondary Role if that helps. I just dont understand which numbers to use to find the variance.

    Maybe if I reword it?

    Leading Role 7females 3males
    Secondary 28females 12 males

    What is the variance among the roles?
    Variation in gender for the leading role:

    E[X] = \frac{7+3}{2} = 5

    E[X^2] = \frac{(7^2 + 3^2)}{2} = 29

    Var(X)= E[X^2] - (E[X])^2 = 29 - (5)^2 = 4

    Now do the same for the second role.
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