math
posted by mary on .
An auditorium has 30 rows with 10 seats in the first row, 12 in the second row, 14 in the third row, and so forth. How many seats are in the auditorium?

looks like an arithmetic series where
a = 10, d=2 and n=30
sum(30) = (30/2)[2(10) + (29)(2)]
= 15[20+58] = 1170
(using the standard formula for the sum of n terms)