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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