A man said, “This girl is the wife of the grandson of my mother”. How is the…

Concept

In blood-relation puzzles, translate a chained description into a family-tree term by counting generations from a common reference person, then apply the standard label — a man is the father-in-law of the person who marries his own son or daughter. A two-step chain such as “grandson of my mother” collapses to a single relation: since the speaker is one generation below his mother, his mother's grandson is one generation below the speaker himself — that is, the speaker's own son, because the statement mentions no sibling of the speaker who could supply an alternative grandson.

Application

1. The man is a son of his own mother — one generation below her, and no sibling of his is mentioned who could also produce a grandson of hers.

2. So “the grandson of his mother” must be two generations below his mother, i.e. one generation below the man himself — this position is the man's own son.

3. The girl is stated to be the wife of that son, so she is the man's daughter-in-law.

4. The father of the girl's husband — the man himself — is, by definition, her father-in-law.

Cross-check

Reading the family tree top-down — the mother, then the man, then the man's son, then the son's wife (the girl) — confirms the same chain: the man is connected to the girl only through his son's marriage, which is exactly the father-in-law relation.

Result

The man is the girl's father-in-law.