Suppose, you are an editor of a magazine. Everyday you
get two letters from your correspondents. Each letter is as likely to be from
a male as from a female correspondent. The letters are delivered by a post-
man, who brings one letter at a time. Moreover, he has a ‘ladies first’ policy;
he delivers letter from a female first, if there is such a letter. Suppose you
have already received the first letter for today and it is from a female corre-
spondent. What is the probability that the second letter will also be from a