Blood relations – single-child logic: Pointing to a girl, Mihir said, "She is the only daughter of my grandfather's only child." How is the girl related to Mihir?

Introduction / Context:
The key phrase is "my grandfather's only child." If the grandfather has only one child, that person must be Mihir's parent. The girl is the only daughter of that parent.

Given Data / Assumptions:

• Mihir is male (typical), but the reasoning does not rely on his gender.
• Only child of grandfather ⇒ parent of Mihir (either father or mother).
• The girl is the only daughter of that parent.

Concept / Approach:
Children of one's parent are siblings. A female child is a sister. Being "only daughter" simply means there is exactly one such sister.

Step-by-Step Solution:

Verification / Alternative check:
If the only child were an uncle/aunt, Mihir wouldn't exist as a grandchild through that line. Hence the only child must be a parent.

Why Other Options Are Wrong:
"Daughter" would make Mihir the parent of the girl; "Niece/Aunt/Cousin" mismatch generational/branch relations.

Common Pitfalls:
Confusing "only child" with "only daughter/son" and assigning to the wrong generation.

Final Answer:
Sister