CCC Common Core Pre-Test Practice

In an arithmetic series, the sum comes from multiplying half the number of terms by the sum of the first and last terms. First term is 4, common difference is 3, and there are 6 terms. The last term is 4 + (6 − 1)×3 = 19. So the sum is 6/2 × (4 + 19) = 3 × 23 = 69. You can also use the formula S_n = n/2 [2a1 + (n − 1)d], which gives 3 × [8 + 15] = 69. Therefore, the total sum is 69.