A coach needs to rank his top 2 players in order. How many possible ways can this be done if there are 25 boys on the team?

Assuming "top two" are ranked first and second:

The coach can choose one out of 25 for the first and 24 for the second.

So there are 25*24=600 ways to choose.

If "top two" simply means the two best, without distinction, then we divide 600 by two to get 300 ways because the choice of the order can be reversed (AB instead of BA).