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The front row of a stadium has 25 seats. Each of the other rows has two more seats than the row in front of it. how many seats are there altogether in the first 20 rows?

i know how to do this in the "long" way but how do you do this is a "shorter" way by finding the pattern? Explain please!!

  • MAth -

    The seat count forms an arithmetic sequence


    where a = 25, d=2

    The sum of the 1st 20 terms is thus
    S20 = 20/2 (2*25 + 19*2) = 880

  • MAth -

    what equation is that?

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