explorer bro, u r correct. yep other probabilities are also there but the main thing is the census taker was confused and hence he asked the lady for other hint. if it were house nr. 11 or whatever, the census taker would have figured out it quite easily and he would not have asked the lady for second hint. since he was confused either the lady has a pair of twins of six years and one child of 1 year or she has one child aged 9 years and one pair of twins aged 2 years. when the lady told him that her eldest child is sleeping, he was sure that she has no twins aged 6 years rather she has an eldest child and hence had solved the problem. good job dude...