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An auditorium has 49 rows of seats. The first row contains 40 seats. As you move to the rear of the auditorium, each row has 3 more seats than the previous row.
-How many seats are in the auditorium?

  • math -

    This is an arithmetic series
    Sum(n) = (n/2)[2a + (n-1)d]
    where a is the first term
    n is the number of terms
    d is the common difference, and
    Sum(n) is the sum of the n terms

    So you want Sum(49)
    with a=40, d=-3 and n = 49

    substitute

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