I have a nuclear family consisting of dad, mom, me and my younger sister. Our birth week i.e. week in which we were born are linear according to our date of birth i.e. my father who is oldest was born on wednesday, my mom on thursday, me on friday and finally my sister(who is youngest) on saturday.
When i was small i used to think this was always the case with any family (this was my definition of being a family) but this is surely not right but actually quite rare to happen. So, i was just wondering given a size of nuclear family consisting of n members (mine is 4) what is the probability that it will have exactly this condition as mine given known number of families in the world(hypothetically).