Q3 of 23 Page 1

Attempt any three of the following sub questions:

There is an auditorium with 3s rows of seats. There are 20 seats in the first row, 22 seats in the second row, 24 seats in the third row and so on. Find the number of seats in the twenty - fifth row.

Seats in each row are 20, 22, 24, …..

∵ The difference between consecutive terms is constant


∴ It is an A.P with common difference = d = 2 and a = 20.


Also, an = a + (n - 1) × d where an is the nth term of A.P.


⇒ a25 = 20 + (25 - 1) × 2


⇒ a25 = 20 + 24 × 2


⇒ a25 = 68


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