Q4 of 23 Page 1

Attempt any two subquestions form the following:

If the second term and the fourth terms of an A.P. are 12 and 20 respectively, then find the sum of first 25 terms:

Given: a2 = 12 and a4 = 20.

Let first term is a and common difference is d, second term is a + d, third term is a + 2d and so on


Then a2 = a + d = 12 ….(1)


And a4 = a + 3d = 20 ….(2)


Now, on subtracting eq (1) from eq(2),


a + 3d – a- d = 20 - 12


⇒ 2d = 8


⇒ d = 4


⇒ a = 12-4 = 8


Hence, sum of the n terms is given as:






⇒ S25 = 1400


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