Question

an auditorium has 32 rows with20 seats in the first row and 6 more seats in each of the successive rows.how many seats are there in the auditorium?

Answer 1

sum of a geometric sequence is
sn=(n(a1+an))/2

32 rows so a32 must be found
a1=20
n=32


first term is 20
common differnce is 6
term to find is 32nd
32th row has 20+6(32-1) or206

S32=(6(32+206))/2
S32=(3(238))
S32=714

answer is 714 seats