Question

In how many ways can 3 oaks, 4 pines and 2 maples be arranged along a property line if one does not distinguish between trees of the same kind

Answer 1

Total of 3+4+2=9 trees.
For 9 different trees, there are 9! ways to plant them.
If 3 of them are indistinguishable, then there are
9!/3! ways.
If another 5 of them are indistinguishable, then there are
9!/(5!3!) ways, and so on.