Posted by Sarah on Wednesday, January 9, 2013 at 1:33am.
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  Steve, Wednesday, January 9, 2013 at 10:58am
The seat count forms an arithmetic sequence
25,27,29...
where a = 25, d=2
The sum of the 1st 20 terms is thus
S20 = 20/2 (2*25 + 19*2) = 880

MAth  Sarah, Wednesday, January 9, 2013 at 11:36pm
what equation is that?
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