This is from GMATPrep,
John wrote 4 letters to four friends and then addressed four envelops, one each for each letter, Assuming all 4 addresses are different what is the probability that only one letter makes it to its envelop.
John wrote 4 letters to four friends and then addressed four envelops, one each for each letter, Assuming all 4 addresses are different what is the probability that only one letter makes it to its envelop.
