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Math Help - yes another one....

  1. #1
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    Unhappy yes another one....

    the sum of the first ten terms of an arithemetic series is 50, and the sum of the first twenty terms is 180. find the common difference and the first term of the series.

    ok this is not going well.... thanks for any help
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  2. #2
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    Quote Originally Posted by pop_91 View Post
    the sum of the first ten terms of an arithemetic series is 50, and the sum of the first twenty terms is 180. find the common difference and the first term of the series.

    ok this is not going well.... thanks for any help
    This is straightforward application of the formulae:

    50 = \frac{10(a + 9d)}{2} .... (1)

    180 = \frac{20(a + 19d)}{2} .... (2)

    Simplify equations (1) and (2) and then solve them simultaneously.
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  3. #3
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    Smile

    ooooooooooh i didnt think of doing that!

    thank you
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