Michigan State University - Diagnostic Exam

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5.7

  •   A section of a stadium has 7 seats in the first row, 10 seats in the second row, 13 seats in the third row, and so on. If the last row has 91 seats, how many seats are in this section?

    a) 2482 b) 1421 c) 1372 d) 82, 810 e) 147

Solution:

We need to find the sum of the arithmetic series S = 7 + 10 + 13 + … + 91. Since the common difference is 3, we can easily find the number of terms, n, in the series.

91 = 7 + (n - 1)3 ⇒ n = 29

We now use the formula

( ) S = 29 7-+-91- 2

Diagnostic:

If you miss this question please review Arithmetic Sequences and Series.

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July 15, 2008