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. 360
**
- Step 1: For an AP with initial term and common difference , the sum of terms is .
- Step 2: Plug in , , and : .
- Step 3: Multiplying out gives .
Answer
360.
Why not the others: '370' evaluates the summation using terms instead of ; '354' omits the factor of in the series formula; '690' adds rather than subtracts the common difference term.
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