Answer
$C(6,3)=20$
Work Step by Step
All the combinations of 6 objects 1,2,3,4,5 and 6 taken 3 at a time is
$123,124,125,126,134,135,136,145,146,156,234,235,236,245,246,256,345,346,356,456$
so using the combination formula we obtain:
$C(6,3)=\frac{6!}{(6-3)!3!}=\frac{6!}{3!3!}=\frac{6\cdot5\cdot4\cdot3!}{3!\cdot3\cdot2\cdot1}=20$
$C(6,3)=20$
