Introducing a man to her husband, a woman said, “His brother’s father is the only son of my grandfather.” How is the woman related to this man?

The correct answer is C. Sister.

Here is the explanation:

The woman’s grandfather has only one son, who is the man’s brother’s father. This means that the man is the woman’s cousin. Cousins are siblings of one’s parents, or the children of one’s aunts or uncles. Therefore, the woman is the man’s sister.

Here is a diagram to illustrate the relationship:

[Diagram of a family tree showing the woman, her husband, and the man]

The woman’s grandfather is the man’s great-grandfather. The woman’s husband is the man’s first cousin once removed. The man is the woman’s first cousin.

Here is a brief explanation of each option:

• A. Mother. The woman is not the man’s mother because the man’s father is the woman’s grandfather’s only son.
• B. Aunt. The woman is not the man’s aunt because the man’s father is the woman’s grandfather’s only son.
• C. Sister. The woman is the man’s sister because the man is the woman’s cousin.
• D. Uncle. The woman is not the man’s uncle because the man’s father is the woman’s grandfather’s only son.
• E. Nephew. The woman is not the man’s nephew because the man is the woman’s cousin.