A payroll clerk addresses five paychecks and envelopes to five different people and randomly inserts the paychecks

Question:

A payroll clerk addresses five paychecks and envelopes to five different people and randomly inserts the paychecks into the envelopes. Find the probability of each event.
(a) Exactly one paycheck is inserted in the correct envelope.
(b) At least one paycheck is inserted in the correct envelope.