Blood Relations
About 7 min · Logical Reasoning · English
Time worked out from the lesson's 473 words at 150 words a minute, plus a minute for each question.
Blood Relations is a core Logical Reasoning topic in SOF IMO that tests your ability to decode family relationships through verbal clues or diagrams. Questions typically present a statement like "A is B's father" or "Pointing to a photograph, X said 'She is my mother's only daughter'" and ask you to identify the relationship between two people. This topic demands careful tracking of gender, generation gaps and familial terminology.
Key ideas
- Reference Person: The individual from whose perspective relationships are described. In "A is B's father," B is the reference. In pointing problems, the speaker is usually the reference.
- Generation Counting: Parents and children differ by one generation, grandparents and grandchildren by two. Siblings are in the same generation. Track generation gaps to avoid confusing nephew with son or uncle with brother.
- Gender Determination: Many relationships specify gender (father, sister, son), but some are ambiguous (parent, sibling, child). Use context clues—possessive forms like "his brother" imply the brother is male, while "her brother" tells you the reference person is female.
- Paternal vs. Maternal Relations: Father's side is paternal (paternal uncle = father's brother), mother's side is maternal (maternal uncle = mother's brother). "Uncle" alone is ambiguous—check whether it's specified as father's or mother's sibling.
- Only Child / Only Son / Only Daughter: "Only" means there are no other siblings of that type. "Only son" means no other sons exist, but daughters may exist. "Only child" means no siblings at all.
Watch out for
- Confusing "only son" with "only child": "Only son" does not rule out daughters. Always check if sisters exist. Fix: Read "only" qualifiers carefully—only son ≠ only child.
- Ignoring gender clues: Assuming "sibling" or "child" without noting gender leads to wrong answers in gender-specific questions. Fix: Mark gender explicitly (M/F) as you decode each person.
- Mixing up generations: Calling a nephew a "son" or an uncle a "brother" because you lost track of generation levels. Fix: Draw a quick family tree with horizontal lines for same generation, vertical for parent-child.
Quick reference
- Draw a simple tree: Horizontal = same generation, vertical = parent-child, use M/F labels.
- "Only son/daughter" ≠ "only child"—siblings of opposite gender may exist.
- Father's/mother's sibling = Uncle/Aunt; their children = Cousins.
- "He is my father's only son" = either me (if I'm male) or my brother (if I'm female).
- In-laws enter through marriage—spouse's family or sibling's spouse.
Check yourself: 3 questions
1. Pointing to a photograph, Rahul said, "She is the daughter of my grandfather's only son." How is the woman in the photograph related to Rahul?
2. Anil introduces Sunita as the wife of the only brother of his father's only daughter. How is Sunita related to Anil?
3. A is the son of B. C, B's sister, has a son D and a daughter E. F is the maternal uncle of D. How is E related to F?
This lesson is cut from the topic's note, not rewritten. Fact-checked on 21 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.
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