Find the sum of each of the following APs: (1/15), (1/12), (1/10),…….. to 11 terms.

Question

Philoid · Accepted Answer

Here, first term = 1/15

Common difference = (1/12) - (1/15) = 1/60

Sum of first n terms of an AP is

S_n = [2a + (n - 1)d]

∴ S₁₁ = [2(1/15) + (11 - 1)(1/60)]

= (11/2) × [(2/15) + (1/6)]

= (11/2) × [(3/10)]

= 33/20

Thus, sum of 11 terms of this AP is 33/20.