Four graduating seniors, A, B, C, and D, have been scheduled for job interviews at 10 a.m. on Friday, January 13, at Random Sampling, Inc. The person- nel manager has scheduled the four for interview rooms 1, 2, 3, and 4, respectively. Unaware of this, the manager s secretary assigns them to the four rooms in a completely random fashion (what else!). What is the probability that
a. All four end up in the correct rooms?
b. None of the four ends up in the correct room?