U={1,2,3,4,5,6,7,8,9,10}
How many 5-element subsets does U have?
I know how to calculate total number of subsets but I can't find the formula for this question in my notes. Any help would be greatly appreciated.
The answer is a combination of 10 choose 5.
$\displaystyle {10 \choose 5} = \frac {10!} {(5!)(10-5)!}$