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Math Help - sigma/summation problem

  1. #1
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    simple problem

    \sum xy -\frac { (\sum x) (\sum y)}{n}
    x= 1, 3, 7, 10
    y= 2, 0, 4, 8
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  2. #2
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    These are bivariate observations, then

    \displaystyle \sum xy -\frac { (\sum x) (\sum y)}{n} =1\times 2 + 3\times 0 +\dots +10\times 8 - \frac{(1+3+\dots +10)(2+0+\dots +8)}{4}= \dots
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  3. #3
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    why did u put n = 4
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  4. #4
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    Well n=4 if the sample is counted as one per (x,y)
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  5. #5
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    Please see rule #2 here. Please do not do this again.

    Both sums are right. What's n? (That's the question you were last on in the other thread, too.)

    -Dan
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  6. #6
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    n represents the number of points of data

    so what i suppose to do
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  7. #7
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by math321 View Post
    n represents the number of points of data

    so what i suppose to do
    Your data set is {(x, y)} = (1, 2), (3, 0), (7, 4), (10, 8).

    -Dan
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  8. #8
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    so therefore n=4
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  9. #9
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    got 36.5
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  10. #10
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    What exactly is your question? Do you not understand what the \sum means? It just means "add them up". I assume that n is 4 here.
    \sum_{n=1}^4 x_ny_n- \frac{\left(\sum_{n=1}^4 x_n\right)\left(\sum_{n=1}^4 y_n\right)}{4}
    = (1)(2)+ (3)(0)+ (7)(4)+ (10)(8)- \frac{(1+ 3+ 7+ 10)(2+ 0+ 4+ 8)}{4}
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