SOLUTION: An auditorium has 20 rows of seats.These are 20 seats in the first row,21 in the second row and 22 in the third row and so on.how many seats are there in all rows?

Question 336210: An auditorium has 20 rows of seats.These are 20 seats in the first row,21 in the second row and 22 in the third row and so on.how many seats are there in all rows?
Answer by galactus(183) (Show Source): You can put this solution on YOUR website!
Did you try just adding them up?. 20+21+22+23+24+....+39
There is a shortcut, though, using the sum of arithmetic sequences.

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