Answer: 9.
- A 6
- B 9
- C 12
- D 15
Correct answer: B. 9
Explanation: Diagonals = nC<sub>2</sub> - n = n(n-1)/2 - n = n(n-3)/2. For n=6: 6×3/2 = 9.
Counting tree for selecting 2 items from {A, B, C} without repetition: 3 x 2 = 6 ordered arrangements.
Concept context
Counting, arrangements, and selections