there are 8 books on a shelf , of which 2 are paperbacks and 6 are hardbacks . how many possible selections of 3 books from this shelf include at least one paperback ?
"approach 1 at - least 1 paper back = total - no paper back 8 c 3 - 6 c 3 = 36 approach 2 at - least 1 paper back = 1 paper back , 3 hard back or 2 paper back 2 hard back = 2 c 1 * 6 c 2 + 2 c 2 * 6 c 1 = 36 answer is c"
subtract(choose(8, 3), choose(6, 3))