An arithmetic series contains 14 numbers. The first number is 12. The last number is 38. What is the sum of the series?

For an arithmetic series, the sum is the number of terms multiplied by the average of the first and last terms. The average is (12 + 38) ÷ 2 = 25, so the sum is 14 × 25 = 350. The correct choice is A, 350.

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