+133 (a) There are n chairs in a row. Find the number of ways of choosing k of these chairs, so that no two chosen chairs are adjacent.
(b) There are 10 chairs in a circle, labelled from 1 to 10. Find the number of ways of choosing 3 of these chairs, so that no two chosen chairs are adjacent.
(c) There are n chairs in a circle, labelled from 1 to n. Find the number of ways of choosing k of these chairs, so that no two chosen chairs are adjacent.
