Question

There is an Auditorium with 27 rows of seat. there are 20 in the First row, 22 second in the second row, 24 seats in the third row and so on. find the number of seats in th 15th row and also find how many total seats are there in the auditorium?

Answer 1

the answer is 48and total 510 seats
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Answer 2

48 in 15th row and
510 seats in total auditorium
 Since the no. of seats in each row of the  auditorium are 20, 22, 24, ......The no. of seats in each row form an A.P.
No. of seats in first row (a) = 20
Difference in no. of seats in two successive rows is (d) = 2
No. of seats in 15th row = t15 = ?
tn = a + (n + 1) d
∴ t15 = a + (15 – 1) d = 20+(14 *2) = 20 + 28 = 48∴  There are 48 seats in 15th row.