Math

An arithmetic series has first term -50 and common difference 4. How many terms are in the series so that the sum of the series first exceeds 100?

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asked by Lucas
  1. Again, use your definition.

    you know S(n) = (n/2)(2a + (n-1)d ), so

    (n/2)(2a + (n-1)d ) > 100

    and you know both a and d

    remember that n has to be a whole number, and you will end up with a quadratic inequality.
    (n/2)(2a + (n-1)d ) = 100 ,
    sub in your values, solve the resulting quadratic for n
    round up your n to the next whole number

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    posted by Reiny

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