Exactly 7 = (more than 2 + less than 3) - (less than 7) = 21 + 31 - 47 = 5
In which city is the number of couples having more than four children and less than seven children is the least?
Out of the couples surveyed by ABC, in how many regions is the number of couples having at least one child lesser than the number of couples having at least one child in P?
Assume that boy and girl babies are equally likely. If a couple have three children, find the probability that at least one is a boy.