Practice!

Sample Problem

Calculate the sum.

2 + 6 + 10 + … + 30 =

Solution

The terms of the sum form an arithmetic sequence with first term 2, last term 30, common difference 4, and number of terms (30 – 2) ÷ 4 + 1 = 8. Using the formula for an arithmetic series, the sum is (2 + 30) × 8 ÷ 2 = 128.