Answer: n(n+1)/2.
- A n(n-1)/2
- B n(n+1)/2
- C n(n+1)/4
- D n²
Correct answer: B. n(n+1)/2
Explanation: 1+2+3+...+n = n(n+1)/2. For n=5: 5×6/2 = 15.
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