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An outdoor amphitheater has 28 seats in the first row, 30 in the second row,

32 in the third row, and so on. There are 39 rows altogether. How many can
the amphitheater seat?

1 Answer

7 votes

Answer: 2574 people

Explanation:

The number of seats in each row forms an arithmetic sequence, where each term increases by 2. The formula for the nth term (a_n) of an arithmetic sequence is given by:an=a1+(n−1)⋅dan​=a1​+(n−1)⋅dwhere:anan​ is the nth term,a1a1​ is the first term,nn is the number of terms,dd is the common difference between terms.In this case:a1=28a1​=28 (number of seats in the first row),d=2d=2 (common difference),n=39n=39 (number of rows).Now we can use the formula to find the number of seats in the 39th row:a39=28+(39−1)⋅2a39​=28+(39−1)⋅2a39=28+38⋅2a39​=28+38⋅2a39=28+76a39​=28+76a39=104a39​=104So, the amphitheater can seat 104 people in the 39th row.To find the total number of seats, you can use the formula for the sum of an arithmetic series:Sn=n2⋅(a1+an)Sn​=2n​⋅(a1​+an​)where:SnSn​ is the sum of the first nn terms.In this case:n=39n=39 (number of rows),a1=28a1​=28 (number of seats in the first row),an=104an​=104 (number of seats in the 39th row).S39=392⋅(28+104)S39​=239​⋅(28+104)S39=19.5⋅132S39​=19.5⋅132S39=2574S39​=2574Therefore, the amphitheater can seat a total of 2574 people.

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