How many different trees are there with four nodes A, B, C and D?
- A. 30
- B. 60
- C. 90
- D. 120
Explanation: Using Cayley's formula $n^{n-2}$ for labeled trees: $4^{2} = 16$. \nIf rooted? $n^{n-1} = 4^3 = 64$?\nIf binary trees? \nQuestion asks "different trees". Usually implies labeled. 16.\nAnswer key has (*). Likely no matching option.