Probability · Question 30 · Hard
Probability question 30
Four letters are placed at random into four envelopes addressed to their four recipients, one letter per envelope. What is the probability that no letter goes into its correct envelope?
- 3/8
- 1/24
- 5/8
- 1/4
Answer and explanation
Answer: A. 3/8
Explanation: The number of arrangements with no letter in its own envelope (derangements of 4) is 9, out of 4! = 24. Probability = 9/24 = 3/8.
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