How many sons does S have?
I. U is mother of S’s son Q, who has two sisters F and E.
II. There are five family members – two males and three females – U’s family. U is wife of S.
From I. We cannot say that Q is only son of S Hence only statement I is not sufficient to answer the question. Statement two alone is also not sufficient to answer the question. But by both statement, we can definitely say that Q is only son of S.