Question

Can anyone help me wit this problem..

Answer 1

Use formula for the number of combinations $\\C_k^n= \frac{n!}{(n-k)!k!} \\ \\n=12, k=2 \\ C_2^{12}= \frac{12!}{(12-2)!2!}= \frac{12!}{10!2!}= \frac{12\times11}{2\times1}=66$