Introducing a man to her husband, a woman said, "His brothers father is the only son of my grandfather." How is the woman related to this man?

Introduction / Context:
This is another layered blood relation statement where the speaker uses a relative, that relative father and then a grandparent in one sentence. The task is to translate that sentence into a simple relationship between the woman and the man she is introducing. These kinds of questions reward a calm, stepwise decoding strategy.

Given Data / Assumptions:

• A woman is speaking to her husband and introducing a man.
• She says, "His brothers father is the only son of my grandfather."
• "My grandfather" refers to the father of one of her parents.
• "Only son of my grandfather" means that this grandfather has exactly one male child.
• We assume usual family structures and no hidden adoptions or remarriages unless mentioned.

Concept / Approach:
The crucial part of the sentence is the chain: his brother → his brothers father → only son of my grandfather. If we can identify who is the "only son of my grandfather" from the womans point of view, then we can link that person to the man being introduced. Once we know that this person is her own father, it becomes straightforward to see that the man is her brother and she is his sister.

Step-by-Step Solution:
Step 1: Let the man being introduced be M. Then "his brother" means a male sibling of M. Both share the same father, call him F.Step 2: "His brothers father" is simply F again, because the man and his brother have the same father.Step 3: The woman says that this father F is "the only son of my grandfather." So F is the only son born to her grandfather.Step 4: From the womans perspective, the only son of her grandfather is normally her father, because a son-in-law is not counted as a son in this wording. So F is her father.Step 5: If F is both the father of M and the father of the woman, M and the woman are children of the same father. That makes them brother and sister.Step 6: The question asks, "How is the woman related to this man?" Since the man is male and the woman shares the same father, she is his sister.

Verification / Alternative check:
Imagine names. Suppose the womans grandfather is Raghav, and his only son is Suresh. Suresh has two children: Meera and Mohan. Meera is the woman speaking, and Mohan is the man being introduced. Meera sentence becomes, "Mohan brothers father is the only son of my grandfather." Mohan brother is still a son of Suresh, and Suresh is indeed the only son of Raghav. This fits perfectly with Meera and Mohan being siblings.

Why Other Options Are Wrong:
The woman cannot be the mother of the man, since she clearly describes his father as the only son of her grandfather, which points to her own father. She is not his aunt, because then the man would be a child of her sibling, not a direct child of the grandfather only son. Cousin also fails because cousins share grandparents but not the same parents. Sister-in-law would require her to be married to his brother, which the sentence does not support.

Common Pitfalls:
Many candidates get stuck at "his brothers father" and treat that as a completely new person instead of realising it loops back to the same father. Another frequent mistake is to treat "only son of my grandfather" as possibly an uncle rather than almost certainly the womans own father. Always start by labelling each person with a symbol and drawing a short diagram if needed.

Final Answer:
The woman is the man sister.