Answer: (n+1)Cr.
- A nC(r+1)
- B (n+1)Cr
- C (n+1)C(r-1)
- D (n-1)Cr
Correct answer: B. (n+1)Cr
Explanation: Pascal identity: nC(r-1) + nCr = (n+1)Cr. Basis of Pascal triangle.
Counting tree for selecting 2 items from {A, B, C} without repetition: 3 x 2 = 6 ordered arrangements.
Concept context
Counting, arrangements, and selections