The first and the last terms of an A.P. are 5 and 45 respectively. If the sum of all its terms is 400, find its common difference.

Question

Philoid · Accepted Answer

First term, a = 5

Last term, l = 45

S_n = 400

[a + l] = 400

n = 16

Now, n = + 1

16 = + 1

16d = 40 + d

15d = 40

d =

Hence, the common difference is