Which of the following represents the sum of the series? 4 plus 7 plus 10 plus 13 plus 16 plus 19 plus 22 plus 25 plus 28 plus 31 plus 34 plus 37 plus 40

The terms increase by 3, from 4 to 40, so there are (40 − 4) ÷ 3 + 1 = 13 terms. The sum of an arithmetic series is the number of terms times the average of the first and last terms: 13 × (4 + 40) ÷ 2. This is choice A, 13 times the quantity (4 + 40) divided by 2.

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