There are 30 rows of seats in the North Wing of a stadium. Each row has 2 seats more than the row in front. The last row has 132 seats. How many seats does the first row have? How many seats are there altogether in the North Wing of the stadium?

Answer 1

the seats form an AP with
a, a+2, a+4, .... , 132
here d=2, n=30
term(30) = a + 29d = 132
a + 29(2) = 132
a = 74

sum of 30 rows = (n/2)( first + last)
= 15(74 + 132) = .....

or

use: Sum(n) = (n/2)(2a + (n-1)d)