Answer: C(m+n, m).
- A m+n
- B C(m+n, m)
- C m × n
- D m! + n!
Correct answer: B. C(m+n, m)
Explanation: Each path needs exactly m right-steps (R) and n up-steps (U): total m+n steps. Choose which m of the m+n steps are R: C(m+n, m). Remaining n are automatically U.
Counting tree for selecting 2 items from {A, B, C} without repetition: 3 x 2 = 6 ordered arrangements.
Concept context
Counting, arrangements, and selections