Assuming that there is no preferred month for giving birth => A person is equally likely to be born in any month of the year. Picking any person at random the probability that he/she is born in winter is 3/12 i.e. No of possible events / No of total possible events = No of months in winter (3)/ Total no of months(12) Now the birthday of the second person whom we randomly choose will be independent of the birthday of the first person. Thus the the probability that the second person is born in winter is the same i.e. 3/12. Total probability = (3/12)*(3/12) = 9/144