Suppose that 4 thank-you notes are written and 4 envelopes are
addressed. Accidentally, the notes are randomly inserted into
the envelopes and mailed without checking the addresses. What is
the probability that all the notes will be inserted into the
correct envelopes?
Let E be the event that all the notes are in the
correct envelope, where the sample space S is the number of
different ways the notes could be inserted in the envelopes. Find
the number of elements in event E, n(E), and the total number
of outcomes in the sample space, n(S).