Question

Determine the sum of the first 20 terms of an arithmetic sequence in which first

terms is 31 and the twentieth term is 109

Answer 1

1400

Explanation:

The average term is the average of the first and last terms.

average term = (31 +109)/2 = 70

The sum of the 20 term is 20 times the value of the average term:

S20 = 20(70) = 1400