Picking a Football Team
How many selections are possible. Typically, a goalkeeper can only play in goal, while an outfield player may play in more than one position. Suppose that the squad contains three goalkeeper. A goalkeeper must be picked for the team, and there must also be a goalkeeper picked as substitute. There are three ways to pick the team goalkeeper and then two ways to pick the substitute, so
\[3 \times 2 =6\]
ways to pick the goalkeepers.There are 10 outfield players remaining to be picked from a choice of 19. Suppose for simplicity that any of these players can play in any position. Each player is to be assigned to a particular position. All the positions are distinct. We can pick 10 players from a possible 19 in
\[{}^19 C_10 =\frac{19!}{10! 9!}\]
ways, and then assign these players to their positions in \[10!\]
ways, so there are \[{}^19 C_{10}\times 10! = \frac{19!}{10! 9!} \times 10! = \frac{19!}{9!}\]
of picking the outfield team.There are
\[6 \times \frac{19!}{9!}\]
ways of picking the team. 
