Question

Find the sum of the first 31 terms of the following series, to the nearest integer.

5, 14,23,...

Answer 1

4340.

Explanation:

14-5 = 9 and 23-14 = 9 so this is an arithmetic series with common difference of 9.

Sum of n terms = (n/2)[2a1 + d(n - 1)]

Here n = 31, d = 9 and a1 = 5.

So, substituting, we have:

Sum of 31 terms = (31/2)[2*5 + 9(31-1)]

= 15.5 * 280

= 4340.