25 – Permutations
Note: In permutations, order is significant.
1. How many permutations are there of a, b, c, d?
2. List the permutations of a, b, c, d.
3. How many 3-permutations are there of a, b, c, d?
4. List the 3-permutations of a, b, c, d.
5. How many permutations are there of 11 distinct objects?
6. How many 5-permutations are there of 11 distinct objects?
For exercises 7-10, determine how many strings can be formed by ordering the letters ABCDE, subject to the following conditions…
7. … contains the substring ACE?
8. … contains the substrings DB and AE?
9. … A appears before D? (example: BCAED, BCADE)
10. … A appears before C and C appears before E?