Multiple choice

The sum of the first n terms of an arithmetic series whose nth term is n can be calculated by the formula n(n + 1)/2. Which one of the following equals the sum of the first eight terms in a series whose nth term is 2n ?

  1. 24

  2. 48

  3. 56

  4. 72

  5. 96
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D Correct answer
Explanation

The nth term is 2n. This is an arithmetic series: 2, 4, 6, 8, 10, 12, 14, 16. Sum = (n/2)(first + last) = (8/2)(2 + 16) = 4 * 18 = 72.

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