In decipher jumbled up description type of questions, a round-about description is given in the form of certain small relationships and direct relationship between the persons concerned is to be deciphered.
Pointing to an old man, Kailash said, "His son is my son`s uncle". How is the old man related to Kailash ?
Kailash's son's uncle -- Kailash's brother.
So, the old man's son is Kailash's brother i.e., the old man is Kailash's father.