CSAT· Prelims
Blood Relations for CSAT: Family Trees and Coded Relations
Learn to crack CSAT blood relation questions with the family-tree method, pointing puzzles, and coded relations, fully solved step by step.
Blood relation questions describe a small family entirely in words and ask how two of its members are related to each other. A typical stem says something like 'A is the brother of B, B is the sister of C, and C is the father of D', and then asks how D is related to A. The difficulty is never the vocabulary; it is holding three or four links in your head at once. In CSAT Paper II, the qualifying paper that needs 33 percent to clear, these questions reward one disciplined habit: converting every sentence into a small family tree before answering anything.
Reading a relation statement link by link
Every relation statement is a chain of links, and each link connects exactly two people. Take 'A is the brother of B'. The link is brother, the subject is A, and the reference person is B. From this one link you learn two facts: A is male, and A and B share parents. Now add 'B is the sister of C': B is female, and B and C share parents, so A, B, and C are siblings. Finally 'C is the father of D': C is male and one generation above D. Now the question 'how is D related to A' is easy: D is the child of C, and A is C's brother, so D is A's nephew or niece. Since D's gender is never given, the safe answer is cannot be determined, a classic UPSC trap.
The golden rule is to work from the reference person outwards. In 'pointing' puzzles such as 'pointing to a photograph, Navdeep said, he is the son of the only son of my mother', start with the pointed person (the boy in the photograph) and climb backwards: the only son of my mother is either Navdeep himself or his brother, depending on Navdeep's gender, and the boy is that person's son. Because the stem never states Navdeep's gender, Navdeep is either the boy's father or his aunt, and the correct option is the one that admits both.
The family-tree method
Draw a quick tree using three conventions and you will never lose track of a chain. Use a square for males and a circle for females; join married couples with a double horizontal line; draw a vertical line from parents down to children; and place siblings on one horizontal level. Generations go top to bottom: grandparents at the top, parents in the middle, children at the bottom. Mark every person's gender the moment a statement reveals it, because an unmarked gender is a signal that the answer may be 'cannot be determined'.
Consider the CSAT-style family set: A is the father of C, D is the son of B, E is the brother of A, and C is the sister of D. How is B related to E? Draw it: A (square) is the father of C (circle). C is the sister of D, so D is A's child too. D is the son of B, so B is D's parent; since A is the father, B must be the mother (circle), married to A. E is the brother of A, so E is A's sibling. B is married to A, and E is A's brother, so B is E's sister-in-law. The tree makes the answer mechanical instead of a memory test.
Coded relations
In coded relation questions, symbols replace relationship words: for example, P minus Q means P is the brother of Q, P plus Q means P is the mother of Q, P percent Q means P is the father of Q, and P cross Q means P is the sister of Q. The method is substitution followed by the family tree. Take the question: which expression shows that A is the maternal uncle of B? Test option (c), A minus M plus N cross B: A minus M means A is the brother of M; M plus N means M is the mother of N; N cross B means N is the sister of B. So M is the mother of N and B, and A is M's brother, which makes A the maternal uncle of B. That matches, so the answer is (c). Always expand every symbol before judging an option, and check options from the target person backwards.
Two phrases deserve special care. Maternal means related through the mother (a maternal uncle is the mother's brother), while paternal means related through the father. And cousin needs no gender: the child of your parent's sibling is your cousin whether male or female, which is why 'cousin' is often the safe answer when genders are unclear.
Worked examples
Example 1 (chain of links). A is the brother of B. B is the brother of C. D is the father of A. Which statement cannot be definitely true? From the first two links, A, B, and C are all brothers, all male, all children of D. Option (a) says B is the brother of A: true. Option (b) says B is the son of D: true. Option (c) says A is the brother of C: true. Option (d) says C is the brother of A: also true on the facts, since C is male. Wait, then which cannot be definitely true? Re-read: 'B is the brother of C' is given, and 'A is the brother of B' is given, so all three are brothers. Every option follows... Actually this question, asked in a UPSC-adjacent set, hinges on option (d): 'C is the brother of A' cannot be definitely true because nothing in the statements says C is male. The first statement makes A male, the second makes B male, but C's gender is never stated: C could be A's sister. So (d) is the answer. The lesson: a sibling link reveals the subject's gender only, never the other person's.
Example 2 (pointing puzzle). Pointing to a photograph of a boy, Navdeep said, 'He is the son of the only son of my mother.' How is Navdeep related to the boy? The 'only son of my mother' is the key phrase. If Navdeep is male, he is that only son, and the boy is his son, making Navdeep the father. If Navdeep is female, the only son is her brother, and the boy is her nephew, making Navdeep the aunt. The stem hides Navdeep's gender, so the answer is either aunt or father. Whenever a pointing puzzle leaves the speaker's gender open, look for the 'either/or' option.
Example 3 (nested description). Introducing a boy, a girl said, 'He is the son of the daughter of the father of my uncle.' How is the boy related to the girl? Unpack from the inside: the father of my uncle is my grandfather (take the uncle as the mother's brother, the usual reading). The daughter of that grandfather is my mother. The son of my mother is my brother. Nested puzzles are solved inside-out, one phrase at a time, and you should write each resolved phrase down before moving outward.
Example 4 (family set). A, B, C, D, and E are members of the same family. There are two fathers, two sons, two wives, three males, and two females. The teacher was the wife of a lawyer who was the son of a doctor. E is not male and is not the wife of a professional. C is the youngest and unmarried, D is the eldest, and B is male. Who are the females? Build generations: D, the eldest, is the doctor and a father. The lawyer is D's son; the teacher is the lawyer's wife, so the teacher is one female and the lawyer's wife is the second wife. That gives two fathers (D and the lawyer), two sons (the lawyer and one more male), three males (D, the lawyer, and C or B), and two females. E is female but not a wife, so E is the doctor's wife? No: the two wives are the teacher and the lawyer's... let me recount cleanly. Males: D (doctor, father), the lawyer (son of D, father), and B (male). Females: the teacher (wife of the lawyer) and E (wife of D). C is the youngest, unmarried, and male (since females are fixed as the teacher and E, and there are exactly three males: D, lawyer, C; B must then be the lawyer). So the females are E and the teacher, and with the teacher being A, the answer is E and A. Family sets are solved by counting constraints: genders, marriages, and generations must all balance.
Common traps
Assuming a gender the stem never gives: 'child', 'sibling', 'cousin', and 'parent' reveal no gender, and the answer is often 'cannot be determined'.
Misreading 'only son' or 'only daughter': the only son of my mother is me if I am male, but my brother if I am female; the speaker's gender decides.
Confusing maternal and paternal: a maternal uncle is the mother's brother, a paternal uncle is the father's brother; coded-relation options exploit exactly this.
In family sets, forgetting that one person can satisfy two roles at once: a man can be both a father and a son, which is how 'two fathers and two sons' fits into three males.
Answering from the wrong end: in 'how is A related to D', A is the subject whose relation you name, so 'A is D's uncle', not the reverse.
Speed tips for the exam hall
Draw the tree immediately, even for short questions; thirty seconds of drawing beats two minutes of re-reading.
Mark gender with square and circle symbols as you go, and circle any person whose gender stays unknown.
In coded relations, expand the symbols into words first, then draw; never try to hold symbols and relations in your head together.
For pointing puzzles, start from the pointed person and resolve the innermost phrase first.
When two options differ only by gender (nephew versus niece), re-check whether the stem actually reveals gender before choosing.
Key Terms
Family tree: a diagram of a family using squares for males, circles for females, double lines for marriages, and vertical lines for parent-child links, drawn with generations from top to bottom.
Sibling: a brother or sister; two people are siblings when they share at least one parent, and the word itself reveals no gender.
Paternal: related through the father, as in paternal uncle (father's brother) or paternal grandmother (father's mother).
Maternal: related through the mother, as in maternal uncle (mother's brother) or maternal aunt (mother's sister).
Cousin: the child of one's parent's sibling; the term applies to both males and females.
Nephew and niece: the son (nephew) or daughter (niece) of one's sibling or sibling-in-law.
In-law: a relative by marriage rather than by blood, as in sister-in-law (the sister of one's spouse, or the wife of one's brother).
Coded relation: a question format in which symbols such as plus, minus, or percent stand for relationship words and must be expanded before solving.
Cannot be determined: the correct answer when the given statements leave a needed fact, usually someone's gender, genuinely open.
Practice questions
Given that: 1. A is brother of B 2. C is father of A 3. D is brother of E 4. E is daughter of B. Then the uncle of D is
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Answer: (A) E is the daughter of B, and D is E's brother, so D is B's child. A is B's brother, which makes A the uncle of D.
Pointing to a photograph of a boy Navdeep said, 'He is the son of the only son of my mother.' How is Navdeep related to that boy?
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Answer: (D) If Navdeep is male, Navdeep is the only son of the mother, and the boy is Navdeep's son (father). If Navdeep is female, the only son is her brother, and the boy is her nephew (aunt). The stem hides Navdeep's gender, so either is possible.
If A is the brother of B; B is the sister of C; and C is the father of D, how is D related to A?
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Answer: (D) A, B, and C are siblings and C is D's parent, so D is the nephew or niece of A. D's gender is never stated, so it cannot be determined.
A is the brother of B. B is the brother of C. D is the father of A. Based on these three statements, which of the following statements cannot be definitely true?
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Answer: (D) The statements make A and B male, but C's gender is never revealed: C could be the sister of A and B. So 'C is the brother of A' cannot be definitely true.
Arjun (male) said: 'This girl is the wife of the grandson of my mother and I do not have any brother and sister'. How is Arjun related to the girl?
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Answer: (D) With no siblings, the grandson of Arjun's mother is Arjun's own son. The girl is that son's wife, so Arjun is her father-in-law.
Introducing a man, a woman said, 'He is the only son of the mother of my mother.' How is the woman related to the man?
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Answer: (C) The mother of my mother is the maternal grandmother, and her only son is the woman's maternal uncle. The woman is therefore his niece.
A is the mother of B. B is the sister of C. C is the brother of D. How is A related to D?
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Answer: (A) A is the mother of B and C (B and C are siblings). C is the brother of D, so D is also A's child, making A the mother of D.
P is the father of R. Q is the wife of P. R is married to T. U is the daughter of R. How is Q related to U?
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Answer: (B) Q is the wife of P and P is the father of R, so Q is R's mother. U is R's daughter, so Q is U's grandmother.
Answer key
Q1 - (a). E is the daughter of B, and D is E's brother, so D is B's child. A is B's brother, which makes A the uncle of D.
Q2 - (d). If Navdeep is male, Navdeep is the only son of the mother, and the boy is Navdeep's son (father). If Navdeep is female, the only son is her brother, and the boy is her nephew (aunt). The stem hides Navdeep's gender, so either is possible.
Q3 - (d). A, B, and C are siblings and C is D's parent, so D is the nephew or niece of A. D's gender is never stated, so it cannot be determined.
Q4 - (d). The statements make A and B male, but C's gender is never revealed: C could be the sister of A and B. So 'C is the brother of A' cannot be definitely true.
Q5 - (d). With no siblings, the grandson of Arjun's mother is Arjun's own son. The girl is that son's wife, so Arjun is her father-in-law.
Q6 - (c). The mother of my mother is the maternal grandmother, and her only son is the woman's maternal uncle. The woman is therefore his niece.
Q7 - (a). A is the mother of B and C (B and C are siblings). C is the brother of D, so D is also A's child, making A the mother of D.
Q8 - (b). Q is the wife of P and P is the father of R, so Q is R's mother. U is R's daughter, so Q is U's grandmother.
Frequently asked questions
What is the single most useful habit for blood relation questions?
Draw the family tree before looking at the options. Use squares for males, circles for females, and vertical lines for parent-child links. Almost every error in this topic comes from trying to hold the chain in memory instead of on paper.
When is 'cannot be determined' the right answer?
When the question asks for a gendered relation (nephew versus niece, uncle versus aunt) but the stem never reveals the needed person's gender. UPSC deliberately writes such questions, so treat an unmarked gender as a warning sign, not a gap to guess across.
How do I solve coded relation questions quickly?
Expand every symbol into plain relationship words first, writing the expansion under each symbol. Then build the tree from the expanded sentence. Attempting to reason directly in symbols is the main source of mistakes.
What does 'maternal uncle' mean, exactly?
Your mother's brother. Maternal always means traced through the mother, paternal through the father. In coded-relation options the two are often swapped to trap hasty readers, so expand carefully.