<p>This question has been driving me crazy >.< Can someone please explain to me how to do it? The answers are supposed to be 1/3 and 3/8.</p>
<p>Four letters and envelopes are addressed to four different people. If the letters are randomly inserted into the envelopes, what is the probability that a. exactly one is inserted in the correct envelope and b. at least one is inserted in the correct envelope?</p>