Answer:
78
Step-by-step explanation:
[tex]nC_k = \frac{n!}{k!(n-k)!}[/tex]
[tex]13 C_{11} = \frac{13!}{11! \times (13-11)!}[/tex]
[tex]= \frac{13!}{11! \times 2!}[/tex]
[tex]= \frac{ 1 \times 2 \times 3 \times 4 \times 5 \times 6 \times 7 \times 8 \times 9 \times 10\times 11 \times 12 \times 13}{(1 \times 2 \times 3 \times 4 \times 5 \times 6 \times 7 \times 8 \times 9 \times 10\times 11 )\times ( 1 \times 2)}[/tex]
[tex]=\frac{12 \times 13}{2} \\\\= 6 \times 13\\\\=78[/tex]
