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

Question

Philoid · Accepted 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