Respuesta :

This is a combination of the form:

[tex]\begin{gathered} C(n,k)=nCk=\frac{n!}{k!(n-k)!} \\ where: \\ n>k \end{gathered}[/tex]

So:

[tex]7C_2=\frac{7!}{2!(7-2)!}=\frac{7!}{2!\cdot5!}=\frac{5040}{2\cdot120}=\frac{5040}{240}=21[/tex]

Answer:

21