An arithmetic progression has first term and common difference . Compute the sum of the first 20 terms, .

Answer and explanation

Correct answer: D.

**Answer: . Why not the others:** mistakenly uses in the multiplication; miscomputes as 16 instead of 8; uses .
  1. Step 1: The sum formula for an arithmetic progression is .
  2. Step 2: Substitute , , and : .

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