2004 · Q81
81. There are three envelopes with three different addresses written on them. Three letters are to be enclosed in these three envelopes such that one letter goes inside one envelope without seeing the address written on any envelope. What is the probability that each of the three letters goes into the envelope with correct address written on it?
MathematicsProbability
- A1/27
- B1/6
- C1/9
- D1/3
Explanation
There are 3! = 6 equally likely ways to place the 3 letters into the 3 envelopes, and only one of them puts every letter into its correctly addressed envelope. The probability is therefore 1/6 — not 1/27, which would wrongly treat each placement as three independent 1/3 chances.