Question

How many subsets with three elements of `A={1,2,3,4,5,6}` containing element "1"?

Answer 1

10 subsets

Explanation:

Since we are interested in subsets of the form: `{1,?,?}`, we need to choose 2 more elements from the remaining 5 elements {2,3,4,5,6}. So, we can count the number of combinations:

`C(5,2)=(5!)/((5-2)!2!)=10` susets