Results 1 to 4 of 4

Math Help - Sums of distributions, and variance

  1. #1
    Member
    Joined
    Jun 2012
    From
    Georgia
    Posts
    191
    Thanks
    25

    Sums of distributions, and variance

    "For tossing a coin, rolling a die, and drawing a card from a standard 52-card deck, respective successes are defined as a head, a 6, and an ace. Find the mean and standard deviation of the total successes of:

    1. 1 coin toss, 1 die roll, and 1 card draw;
    2. 3 tosses, 2 rolls, and 1 draw.

    The means are easy, but I can't get the right numbers for the standard deviations. And yes, I am remembering to work with variances, then square root to get back to the s.d. My respective s.d.s are 0.6469 and 1.028, but the back of the book has 0.68 and 1.05. Please help.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Sep 2012
    From
    Australia
    Posts
    3,879
    Thanks
    697

    Re: Sums of distributions, and variance

    Hey phys251.

    Did you use 1/(n-1) instead of 1/n for the variance (and standard deviation) calculations?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Jun 2012
    From
    Georgia
    Posts
    191
    Thanks
    25

    Re: Sums of distributions, and variance

    Quote Originally Posted by chiro View Post
    Hey phys251.

    Did you use 1/(n-1) instead of 1/n for the variance (and standard deviation) calculations?
    Oh goodness. I'm supposed to take a SAMPLE standard deviation, not a population standard deviation, aren't I?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Joined
    Sep 2012
    From
    Australia
    Posts
    3,879
    Thanks
    697

    Re: Sums of distributions, and variance

    You do if you have a sample and not a population.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 1
    Last Post: October 4th 2013, 05:09 AM
  2. Replies: 1
    Last Post: February 22nd 2013, 09:12 AM
  3. variance of the sample variance
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: February 8th 2011, 08:35 PM
  4. How to get new variance given old variance and average
    Posted in the Advanced Statistics Forum
    Replies: 0
    Last Post: November 23rd 2010, 05:39 AM
  5. Variance of the population variance.
    Posted in the Advanced Statistics Forum
    Replies: 2
    Last Post: November 10th 2008, 09:07 AM

Search Tags


/mathhelpforum @mathhelpforum