Problem source

A school has $n$ pupils, of whom $r$ play hocket, where $n\geqslant r\geqslant2.$
All $n$ pupils are arranged in a row at random. 
\begin{questionparts}
\item What is the probability that there is a hockey player at each end
of the row?
\item What is the probability that all the hockey players are standing together?
\item By considering the gaps between the non-hockey-players, find the probability
that no two hockey players are standing together, distinguishing between
cases when the probability is zero and when it is non-zero. 
\end{questionparts}