1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Statistics: Mean values

  1. Jan 16, 2009 #1
    1. The problem statement, all variables and given/known data
    Hi all.

    Lets say I have two variables yk and xk. I also have two mean values given by:

    <y_k^2> = \frac{1}{N}\sum_1^N{y_k^2} \quad \text{and} \quad <x_k^4> = \frac{1}{N}\sum_1^N{x_k^4}.

    Now I am looking at the expression (<xk4> <yk2>)1/2.

    Question: Is it correct that:

    <y_kx_k^2> = \sqrt{<x_k^4><y_k^2>}.

    Personally, I don't think so, because ultimately it would mean that I would have to make two sums into one sum, which I can't.. but I am in doubt.

    Thanks in advance.

  2. jcsd
  3. Jan 16, 2009 #2


    Staff: Mentor

    Per your notation (< ... >), <yk2> denotes the mean of the squared values of yk.

    So <xk4yk2> would be the sum of the products of xk4yk2, divided by N, which is not the same as (<xk4> <yk2>)1/2.
    The latter would just be the square root of (the mean of the x^4 terms times the mean of the y^2 terms).
  4. Jan 16, 2009 #3
    Yeah, just what I thought.. so they are not the same.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook