Concept 6.5 (Counting Permutations). Let S = {a, b, c, d, e, f }.

How many 1. 4-permutations are there of S ?

2. 4-permutations are there of S such that a does not appear?

3. 4-permutations are there of S such that a does appear?

4. 6-permutations are there of S that end with a or have d in the second-leftmost position?

5. 6-permutations are there such that a and d are never next to one another?

6. 4-permutations are there such that a is followed by c