The first term of an arithmetic progression is and its common difference is . What is the sum of its first terms?

Answer and explanation

Correct answer: C. 198

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  1. Step 1: The sum of an arithmetic progression is determined by .
  2. Step 2: With , , and , we evaluate .
  3. Step 3: Simplifying the product gives .
Answer
198.
Why not the others: '207' evaluates the summation using terms instead of ; '423' omits the factor of in the series formula; '193' adds rather than subtracts the common difference term.

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