In this case, the order does not matter and we can not replace it.
Hence, we need to use a combination for this case.
The equation is given by:
[tex]nCx=\frac{n!}{x!(x-n)!}[/tex]
Where n represents the total number of friends and x represents the number of the group.
Then,
n = 15 friends
x = choose 4 of them
Replacing:
[tex]15C4=\frac{15!}{4!(15-4)!}[/tex]
Simplify:
[tex]\begin{gathered} 15C4=\frac{15!}{4!11!} \\ 15C4=1365 \end{gathered}[/tex]
Hence, Jhon can choose them 1365 ways.
The correct answer is option d.
