Out of 5 tickets you have to use 1 ticket for your own and remaining 4 for other friends.
So basically you have to find how many ways you can pick 4 friends out of total 9 friends.
This can done using combination formula
[tex] C(n,r)=\frac{n!}{r!*(n-r)!} [/tex]
That formula means selecting r people from n people.
We are choosing 4 out of 9 so r=4, n=9
now plug those values into above formula
[tex] C(9,4)=\frac{9}{4!*(9-4)!} [/tex]
[tex] C(9,4)=\frac{9!}{4!*(5)!} [/tex]
[tex] C(9,4)=\frac{362880}{24*120} [/tex]
[tex] C(9,4)=126 [/tex]
So there are 126 ways to form arequired team.
