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-   -   Summation xiyi (https://www.askmehelpdesk.com/showthread.php?t=422637)

  • Dec 6, 2009, 11:41 AM
    kabaker
    summation xiyi
    This is from my lecture notes and I should have clarified before leaving class.

    How do you find the summation (xi - x bar) (yi - y bar) = 6640 summation (xi - xbar)2= 1239.88

    x: 2 8 16 22 25 34 35 39
    y: 30 75 165 200 110 250 225 225
  • Dec 6, 2009, 12:29 PM
    Unknown008

    Do you mean two separate things here?



    and



    ?

    Because that seems as:

    If I'm right, then what you have to do is:
    1. Find x bar and y bar, the mean of x and y respectively.
    2. x_i is each value that x contains. x_i - x bar is (2 - x bar) or (8 - x bar), etc.
    Summation of (x_i - x bar) is the mean, removed from each of the terms in x.

    Here, it is:
    (2 - x bar) + (8 - x bar) + (16 - x bar) + (22 - x bar) + (25 - x bar) +... + (39 - x bar)

    3. The same goes for (y_i - y bar).

    For the first one, multiply each result of (x_i - x bar) with (y_i - y bar) then add them together.

    For example, do (2 - x bar)(30 - y bar) + ( 8 - x bar)(75 - y bar)

    For the second one, square each (x_i - x bar) then add them up.

    I just checked them, and I got the answers right :)

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