Q. 115.0( 1 Vote )

The 5th term of an AP is 20 and the sum of its 7th and 11th terms is 64. The common difference of the AP is
A. 4

B. 5

C. 3

D. 2

Answer :

Let a be the first term and d be the common difference.


Given: a5 = 20


a7 + a11 = 64


Now, Consider a5 = 20


a + 4d = 20 ……………(1)


Consider a7 + a11 = 64


a + 6d + a + 10d = 64


2a + 16d = 64 …………(2)


Subtract twice of equation (1) from (2), we get,


8d = 24


d = 3

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