Q. Three letters, to each of which corresponds an envelope, are placed in the envelopes at random. The probability that all the letters are not placed in the right envelopes, is
A) 1/6
B) 5/6
C) 1/3
D) 2/3
Explanation
(b)
Three letters can be placed in 3 envelopes in 3! ways, whereas there is only one way of placing them in their right envelopes. So. Probability that all the letters are placed in the right envelopes$= \frac{1}{3!}$
Hence, required probability$= 1 - \frac{1}{3!} = \frac{5}{6}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.