Homework Help: math

Posted by Anonymous on Tuesday, November 3, 2009 at 1:15am.

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 - Reiny, Tuesday, November 3, 2009 at 7:31am
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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