The first term of an arithmetic progression is 5 and the common difference is 7. Find the sum of the first 9 terms.
Answer and explanation
Correct answer: D. 297
- Step 1: Use S = n/2 [2a + (n - 1)d] = 9/2 x [10 + 8 x 7]. Step 2. = 297. Answer: 297. Why not the others: 61: That is only the 9th term, not the sum. 304: That is off by one common difference. 290: That is off by one common difference in the other direction.
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