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Math Help - 2 problems, thanks!

  1. #1
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    2 problems, thanks!

    1. 0 + 1 - 2 + 3 - 4...100=___

    2. 0 + 1 + 2 + 3 + 4 +...+ 98 + 99 + 100=_____


    state solution and explanation of how you got to the solution,

    thanks!
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  2. #2
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    Quote Originally Posted by Alana0001 View Post
    1. 0 + 1 - 2 + 3 - 4...100=___

    2. 0 + 1 + 2 + 3 + 4 +...+ 98 + 99 + 100=_____


    state solution and explanation of how you got to the solution,

    thanks!
    In both cases you're expected to know and use the formula for the sum of an arithmetic series.

    Note that the first one can be re-arranged as (1 + 3 + 5 + .... + 99) - (2 + 4 + 6 + ...... + 100).
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  3. #3
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    Quote Originally Posted by Alana0001 View Post
    1. 0 + 1 - 2 + 3 - 4...100=___

    2. 0 + 1 + 2 + 3 + 4 +...+ 98 + 99 + 100=_____


    state solution and explanation of how you got to the solution,

    thanks!
    Use these formulas:
    1+2+3+...+n=\frac{n(n+1)}{2}
    1+3+5+...+n=\left(\frac{n+1}{2}\right)^2
    Last edited by ely_en; September 2nd 2008 at 11:00 PM.
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