Answer: (10n+1 − 9n − 10)/9.
- A (10n+1 − 9n − 10)/9
- B (10n+1 − 10)/9 + n
- C (10n+1 − 9n − 10)/81
- D 10n+1/9 − n
Correct answer: A. (10n+1 − 9n − 10)/9
Explanation: Each term is 10k − 1, so the sum is (10n+1 − 10)/9 − n = (10n+1 − 9n − 10)/9. Check n = 2: 108.
Bar heights for AP 2, 5, 8, 11 with the common difference d=3 marked between consecutive terms.
Concept context
Arithmetic progressions, geometric progressions, and sums