Question

Three letters are dictated to three persons and an envelope is addressed to each of them, the letters are inserted into the envelopes at random so that each envelope contains exactly one letter. find the probability that at least one letter is in its proper envelope.

Answer 1

total no of cases are 6 (3!)
the ways it can go in wrong envelope are 2 ways
1goesto2,2goes3,3goes1 or 1to3,3to2,2to1
ans = 4/6