Blood Relations
About 7 min · Logical Reasoning · English
Time worked out from the lesson's 511 words at 150 words a minute, plus a minute for each question.
Blood Relations is a staple of logical reasoning in competitive exams, including the SOF NSO. The topic tests your ability to decode family relationships described in words or pointing statements and translate them into a clear family tree. You'll be asked to identify how person A is related to person B after a chain of relationships is given, or determine the gender and exact relationship of a hidden person.
Key ideas
- Generation levels matter. Always track whether people are in the same generation (siblings, cousins), one generation apart (parent-child), or two apart (grandparent-grandchild). Mixing generations is the fastest route to wrong answers.
- Gender is critical. Many relationships change meaning with gender: brother vs sister, uncle vs aunt, grandson vs granddaughter. If gender is not stated, consider both possibilities or look for clues in pronouns (he/she, his/her).
- Paternal vs maternal side. Uncle can mean father's brother or mother's brother. Aunt can be father's sister or mother's sister. The prefix "maternal" or "paternal" clarifies, but if omitted, check the problem context.
- Spouse links connect families. If A is married to B, then A's parents become B's in-laws, and B's siblings become A's brothers/sisters-in-law. Keep track of marriages to avoid dead ends.
- Use symbols or abbreviations. In rough work, draw circles for females, squares or triangles for males, and use lines to show parent-child or marriage links. Or use letters with +/- or M/F labels. Speed comes from a consistent notation system.
Watch out for
- Confusing "only son" with "son." "Only son" means no other sons exist; there can still be daughters. Students often assume "only son" = "only child," leading to wrong answers. → Fix: Only son = no brothers, but sisters possible. Only child = no siblings at all.
- Ignoring gender pronouns. A problem says "his father" and you assume the person is male, but later "her brother" appears. Inconsistent tracking of he/she/his/her causes contradictions. → Fix: Underline or note gender clues (he, she, his, her) as you read. If ambiguous, write M/F next to the name.
- Mixing maternal and paternal lines. "Uncle" without a qualifier could be either side. Students pick one arbitrarily and get tripped up. → Fix: If the problem doesn't specify, consider both. Often, additional clues (like "my father's family") will clarify.
Quick reference
- Father's/Mother's brother = Uncle; Father's/Mother's sister = Aunt.
- Brother's/Sister's child = Nephew (male) or Niece (female).
- Only son/daughter ≠ only child; watch for siblings of the opposite gender.
- "My mother's daughter" = me (if female) or my sister, never my mother.
- Use rough diagrams: circles for females, boxes for males, lines for parent-child and marriage.
Check yourself: 3 questions
1. Pointing to a photograph, Rajesh says, "She is the daughter of my grandfather's only son." How is the woman in the photograph related to Rajesh?
2. A is the brother of B. B is the sister of C. C is the father of D. How is D related to A?
3. Introducing a man, a woman said, "His wife is the only daughter of my mother." How is the woman related to the man?
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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