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Math Help - Summation notation

  1. #1
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    Summation notation

    If I had 12 measurements: 30, -38, -70, -78, 32, 73, 49, -88, 29, 32, 42, 6, and they were labeled x1, x2, x3 etc, how would I find the following?

    Find .

    I added all the numbers, and came up w/19. Then I took x1 which was 30 and added 49 to that and then multiplied that by 19 and came up w/1501 which is the wrong answer. Can anybody help me w/this? Thank you.
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  2. #2
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    Quote Originally Posted by Y-rag View Post
    If I had 12 measurements: 30, -38, -70, -78, 32, 73, 49, -88, 29, 32, 42, 6, and they were labeled x1, x2, x3 etc, how would I find the following?

    Find .

    I added all the numbers, and came up w/19. Then I took x1 which was 30 and added 49 to that and then multiplied that by 19 and came up w/1501 which is the wrong answer. Can anybody help me w/this? Thank you.

    Would this be 19+49= 68? Would that be the answer?
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  3. #3
    No one in Particular VonNemo19's Avatar
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    \sum_{i=1}^{12}(x_i+49)=\sum_{i=1}^{12}x_i+\sum_{i  =1}^{12}49

    Now since \sum_{i=1}^{12}49=49(12)

    and

    \sum_{i=1}^{12}x_i=30+(-38)+(-70)+(-78)+32+73+49+(-88)+29+32+42+6

    we have

    \sum_{i=1}^{12}(x_i+49)=30+(-38)+(-70)+(-78)+32+73+49+(-88)+29+32+42+6+[12(49)]<br /> <br />

    Can you handle it from here buddy?
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  4. #4
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    VonNemo, I get 607. Does that seem like I handled it?

    This is worse than learning to play the piano and I've never done that but I can guess how painful it would be.
    Last edited by Y-rag; May 27th 2009 at 08:48 PM.
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  5. #5
    No one in Particular VonNemo19's Avatar
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    I'm getting 607. Try again. Always check your work, man.
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  6. #6
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    I corrected myself after I sent the wrong number, I got 607 also. Dumb mistake on my part. Thank you immensely.
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