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.
In the NSO, 1–2 questions typically appear from this topic, often mixed with verbal or analytical reasoning. Mastery requires two skills: understanding the vocabulary of relationships (uncle, maternal grandmother, sister-in-law, etc.) and quickly building a mental or rough diagram of the family tree. Most mistakes come from confusing paternal and maternal sides or misjudging gender from ambiguous descriptions. With practice, these become quick 30-second solvers.
The problems come in two main formats: **family-tree style** (A is the son of B, B is the sister of C — how is A related to C?) and **pointing-style** (A points to B and says "Her mother is my mother's daughter" — who is B to A?). Both require systematic step-by-step decoding. Let's break down the essentials.
Key Concepts
**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.
**Only-child and sibling clues.** "Only son" or "only daughter" means no other children of that gender in the family. This narrows possibilities sharply in complex puzzles.
**"My mother's daughter" = me or my sister.** In pointing problems, always simplify possessive chains step by step. "My mother's daughter" is either the speaker or the speaker's sister, never the mother herself.
**Count carefully in multi-step chains.** If A is the father of B, and B is the father of C, then A is the grandfather of C — two generations up. Track each link to avoid off-by-one errors.
Key Facts
1. **Father's brother = Uncle (paternal uncle).** Father's sister = Aunt (paternal aunt). 2. **Mother's brother = Uncle (maternal uncle).** Mother's sister = Aunt (maternal aunt). 3. **Brother's wife = Sister-in-law.** Sister's husband = Brother-in-law. 4. **Husband's/wife's parents = Father-in-law / Mother-in-law.** 5. **Husband's/wife's siblings = Brother-in-law / Sister-in-law.** 6. **Son's wife = Daughter-in-law.** Daughter's husband = Son-in-law. 7. **Niece = brother's or sister's daughter.** Nephew = brother's or sister's son. 8. **Cousin = uncle's or aunt's child** (can be maternal or paternal cousin). 9. **Grandmother = mother's mother or father's mother.** Grandfather similarly. 10. **Only son/only daughter** means no siblings of that gender exist in that family unit.
Worked Examples
**Example 1 (Family-tree style):** Pointing to a photograph, Ramesh says, "She is the daughter of my grandfather's only son." How is the woman related to Ramesh?
*Solution:* Break it down step by step.
"My grandfather's only son" = Ramesh's father (since "only son" means the grandfather has exactly one son, who must be Ramesh's father).
"She is the daughter of [Ramesh's father]" = Ramesh's sister.
**Answer:** Sister.
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**Example 2 (Pointing-style):** A man pointing to a woman says, "Her mother is my mother's daughter." What is the woman to the man?
*Solution:* Simplify "my mother's daughter."
"My mother's daughter" = the man himself (if he's male and an only child) OR the man's sister.
Since the problem says "her mother," the woman's mother is either the man himself (impossible, men can't be mothers) or the man's sister.
If the woman's mother is the man's sister, then the woman is the man's sister's daughter = niece.
**Answer:** Niece.
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**Example 3 (Chain reasoning):** A is the father of B. B is the sister of C. C is the mother of D. How is A related to D?
*Solution:* Build the tree:
A is the father of B (and also of C, since B and C are siblings — both are A's children).
C is the mother of D, so D is A's grandchild.
Gender of D is not given, so answer is **grandfather** if we must state A's relation, or "D is A's grandson or granddaughter."
**Answer:** A is the grandfather of D (or D is A's grandchild).
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Common Mistakes
1. **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.
2. **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.
3. **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.
4. **Forgetting in-laws.** A is married to B; problem asks how A is related to B's sister. Students forget that B's sister is A's sister-in-law. → **Fix:** Mark marriages with a connecting line in your diagram. Spouse's relatives become in-laws.
5. **Misinterpreting "my mother's daughter."** Students think it means "my mother." → **Fix:** "My mother's daughter" = a daughter of my mother, which is either me (if I'm female) or my sister. Never the mother herself.
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?
Q2 · Blood Relations · MEDIUM
A is the brother of B. B is the sister of C. C is the father of D. How is D related to A?
Q3 · Blood Relations · EASY
Introducing a man, a woman said, "His wife is the only daughter of my mother." How is the woman related to the man?
Q4 · Blood Relations · MEDIUM
P + Q means P is the father of Q. P - Q means P is the mother of Q. P × Q means P is the brother of Q. P ÷ Q means P is the sister of Q. If A + B - C × D ÷ E, how is A related to E?
Q5 · Blood Relations · HARD
Arjun said, "This girl is the wife of the grandson of my mother." How is Arjun related to the girl?