A man write five letters, one each to A, B, C, D, and E. Each letter is placed in a separate envelope and sealed. He then addresses the envelopes, at random, on each to A, B, C, D, and E.

  1. Find the probability that the letter to A is in the correct envelope and the letter to B is in an incorrect envelope.
  2. Find the probability that the letter to A is in the correct envelope, given that the letter to B is in an incorrect envelope.
  3. Find the probability that both of the letter to A and B are in incorrect envelopes.

Ans: \frac{3}{20}; \frac{3}{16}; \frac{13}{20}

Leave a Reply