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?