How to Solve Blood Relation Questions: 7 Worked Examples

Blood relation questions have one repeatable shortcut: draw the family tree before reading the answer options. Placement tests from TCS NQT to Infosys SP include blood relation questions in their logical reasoning sections. Students who sketch the chain before checking the options answer them faster and with fewer errors than those who hold the entire chain in working memory. The seven worked examples below cover the main structures you will encounter, each re-derived from first principles.

Draw the tree before anything else

Three steps handle every blood relation question:

• Step 1: Draw one box per named person. Write M or F beside the name if gender is stated or clearly implied by the problem.
• Step 2: Draw a downward arrow from parent to child for each parent-child link. Connect married couples with a horizontal line between their boxes.
• Step 3: Read the relationship by tracing the path between the two people the question asks about.

Two rules keep the tree accurate:

• Never assume gender. If the question says “sibling” or “child” without specifying, leave the box unmarked until a later statement in the problem confirms it.
• In dialogue questions that use “my father’s sister” or similar first-person phrasing, the speaker is always the first node. Anchor every subsequent link at the speaker, not at the person being described.

For the six structural patterns that appear across campus placement tests, see blood relation questions for placement tests.

Direct chains and generation gaps

Example 1 — Two-step chain

• Q: A is B’s father. B is C’s mother. How is A related to C?
• Step 1: A is one generation above B.
• Step 2: B is one generation above C.
• Step 3: A is two generations above C. Two parent-child links above = grandparent.
• Answer: A is C’s grandfather.

Example 2 — Sibling shortcut

• Q: P is Q’s parent. Q is R’s sibling. R is S’s parent. How is P related to S?
• Step 1: P is one generation above Q.
• Step 2: Q and R are siblings; siblings share the same parents. P is therefore also R’s parent.
• Step 3: R is one generation above S.
• Step 4: P is two generations above S.
• Answer: P is S’s grandparent.

Example 3 — Generation arithmetic

• Q: D is E’s grandson. F is D’s son. How is E related to F?
• Step 1: “D is E’s grandson” means E is 2 parent-child links above D.
• Step 2: “F is D’s son” means F is 1 parent-child link below D.
• Step 3: E is 2 + 1 = 3 parent-child links above F.
• Three links above = great-grandparent.
• Answer: E is F’s great-grandmother.

Generation arithmetic rule: count parent-child links in the chain. One link above = parent, two = grandparent, three = great-grandparent. The same count applies downward for children, grandchildren, and great-grandchildren.

Coded relations

Coded questions give you a symbol key before the expression. Decode each symbol into plain English before drawing the tree. Keep the key visible while you work through each statement.

Example 4 — “P+Q means Q is the father of P” style

• Q: Key: A + B means B is the father of A. Expression: M + N + R. How is R related to M?
• Decode M + N: N is M’s father. Place N one generation above M.
• Decode N + R: R is N’s father. Place R one generation above N.
• R is N’s father and N is M’s father: R is two links above M.
• Answer: R is M’s grandfather.

Example 5 — Three-symbol key

• Q: Key: P * Q means P is the mother of Q; P - Q means P is the brother of Q; P # Q means P is the husband of Q. Expression: A * B - C # D. How is A related to D?
• Decode A * B: A is B’s mother.
• Decode B - C: B is C’s brother. B and C are siblings, so A is also C’s mother (siblings share the same parents).
• Decode C # D: C is D’s husband. D is C’s wife.
• A is C’s mother; D is C’s wife. A is the mother of D’s husband.
• Answer: A is D’s mother-in-law.

The cousin trap

Cross-generation questions are where wrong answers cluster most. The most frequent error is treating a cousin as a sibling. The example below is the exact category where this error appears.

Example 6 — Cousin, not sibling

• Q: Ravi’s father is the only son of Ravi’s paternal grandfather. Ravi’s grandfather’s only daughter is Priya. Priya’s son is Arjun. How is Arjun related to Ravi?
• Step 1: Ravi’s paternal grandfather has two children: Ravi’s father (son) and Priya (daughter).
• Step 2: Priya is Ravi’s father’s sister. That makes Priya Ravi’s paternal aunt.
• Step 3: Arjun is Priya’s son, so Arjun is the son of Ravi’s aunt.
• Step 4: The child of a parent’s sibling is a cousin, not a sibling.
• Answer: Arjun is Ravi’s cousin.

The wrong answer, “brother,” comes from reading “grandfather’s daughter” as equivalent to “my parent.” She is not. Priya is the grandfather’s daughter through a different branch from Ravi’s father. When a grandparent’s other child (not your direct parent) appears in the chain, the next generation down from that child is always your cousin. Draw two separate branches from the grandparent node whenever the grandparent has more than one child.

In-law chains

In-law links pass through a marriage. The method: find who is married to whom first, then follow the blood chain from the married person’s family.

Example 7 — Mother-in-law chain

• Q: A is B’s mother-in-law. B is married to C. C is D’s father. How is A related to D?
• Decode “A is B’s mother-in-law”: A is the mother of B’s spouse.
• B is married to C, so C is B’s spouse. A is C’s mother.
• C is D’s father. A is the mother of D’s father.
• Answer: A is D’s grandmother.

Four errors that flip your answer

Most wrong answers in blood relation questions come from one of four moves:

• Assuming gender without a cue. If the problem says “sibling” or “child” without a gender marker, keep the box unmarked until a later statement confirms it.
• Losing the narrator anchor. In dialogue questions, the speaker is always Node 1. Students who start the tree at the described person instead of the speaker end up with an inverted family tree.
• Calling a cousin a sibling. Draw two branches from a grandparent node when that grandparent has more than one child. Children of different branches who share the same grandparent are cousins.
• Crossing in-law and blood. “Daughter-in-law of my mother” and “daughter of my mother” lead through entirely different chains. Trace to the married person first, then cross the marriage link to reach their family of origin.

For other logical reasoning types that use the same step-by-step constraint method, see number analogy patterns for logical reasoning.

The generation arithmetic in these examples (counting parent-child links to identify a great-grandparent) is a constraint-satisfaction pattern where each link is a state transition, and losing track of one flips the final answer. That same multi-step reasoning structure appears in LLM prompt chains. TinkerLLM at ₹299 lets you run those chains on real language models and observe where the reasoning holds or breaks.