An auditorium has 30 rows of seats. It has 20 seats on the first row, 24 seats on the second row, 28 seats on the third row, and so on.

Question

An auditorium has 30 rows of seats.  It has 20 seats on the first row, 24 seats on the second row, 28 seats on the third row, and so on.
	1. How many seats are there in the 20th row?
	2. How many seats are there in the whole auditorium?

Steve · Accepted Answer

You have an arithmetic progression where a = 20 d = 4 T20 = 20+19*4 = 96 S30 = 30/2(2*20+29*4) = 2340