Blood Relations

Blood relation problems sound intimidating, but they’re really just puzzles about family trees. We’re given clues about how people are related, and we need to figure out a specific relationship. The secret weapon? Draw a family tree. Always. Even for “easy” problems. The moment we start solving in our heads, we make mistakes.

Relationship Terminology

Before we jump into problems, let’s make sure we know the relationship vocabulary. This is the foundation.

The Family Tree Diagram Technique

This is our main tool. Here’s how we draw family trees:

The golden rule: Always draw the family tree from the clues, placing people at the correct generation level. Start with the clue that gives us the most information.

Decoding Coded Relationships

The hardest part of blood relation problems isn’t the family tree — it’s understanding sentences like “A is the son of B’s father’s only daughter.” Let’s break down the approach.

Work from inside out. Start from the innermost relationship and expand.

Worked Examples

Example 1: Simple relationship chain

Pointing to a photograph, A says “He is the son of my father’s only son.” Who is the person in the photo?

Let’s decode from inside out:

1. “my father’s only son” — A’s father has only one son. That’s A himself.
2. “the son of A” — that’s A’s son.

The person in the photograph is A’s son.

Example 2: Introduction problem

A introduces B saying “She is the daughter of the only son of my father’s wife.” How is B related to A?

Decode step by step:

1. “my father’s wife” = A’s mother
2. “only son of A’s mother” = A himself (A is the only son of his mother)
3. “daughter of A” = A’s daughter

B is A’s daughter.

Example 3: Multi-person family tree

Read the clues and determine: How is D related to A?

Clues:

• A is the father of B
• B is the sister of C
• C is the husband of D

Let’s build the family tree:

Generation 1: A (male, father)

Generation 2: B (female, A’s daughter) and C (male, A’s son — since B is C’s sister, they share parents)

C is married to D. So D is C’s wife.

Now: D is married to C, who is A’s son. So D is A’s daughter-in-law.

Example 4: Complex coded relationship

A says to B: “Your mother’s husband’s sister is my aunt.” How are A and B related?

Decode:

1. “B’s mother’s husband” = B’s father
2. “B’s father’s sister” = B’s aunt (bua)
3. “B’s aunt is my (A’s) aunt”

If they share the same aunt (their father’s sister), then A and B’s fathers are siblings (brothers). This means A and B are cousins.

But wait — there’s another possibility. If A and B have the same father, then A’s father’s sister is also B’s father’s sister. In that case, A and B are siblings (brother/sister).

In exam questions, they usually make it clear whether they’re siblings or cousins based on additional context. If the question says “A and B are not siblings,” then they’re cousins.

Example 5: Pointing-to-a-person problem

Pointing to a woman, Ramesh says “She is the daughter of my grandfather’s only child.” How is the woman related to Ramesh?

Decode:

1. “Ramesh’s grandfather’s only child” = Ramesh’s father (grandfather had only one child, that’s Ramesh’s parent — and since it’s “child” with a son who became Ramesh’s father)
2. “daughter of Ramesh’s father” = Ramesh’s sister

The woman is Ramesh’s sister.

Important: We assumed the “only child” is male (Ramesh’s father). If the only child were female (Ramesh’s mother), the answer could be different. But since Ramesh exists as the child of this person, and the grandfather is paternal, the only child is Ramesh’s father.

The Systematic Approach

For complex problems with many clues, follow this method:

1. List all people mentioned — make a note of any gender information given
2. Start with the most definite clue — something like “A is the father of B” (gives us gender + relationship)
3. Place people on generation levels — same generation = same horizontal line
4. Add clues one by one — draw lines for each relationship
5. Use elimination — if only one arrangement satisfies all clues, that’s the answer
6. Watch for “only” — it’s the most important word. “Only son” means no brothers, “only child” means no siblings at all.

Common Traps

• Gender assumption: “A is the parent of B” — we don’t know if A is father or mother
• “Only” is key: “Father’s son” could be the person themselves OR their brother. But “father’s ONLY son” must be the person themselves.
• In-laws vs blood relations: “A’s brother-in-law” could mean A’s spouse’s brother OR A’s sibling’s husband — two different people!
• Same name, different roles: In complex problems, don’t confuse who is being described

Common Exam Variations

• Pointing to a photograph — “This person is the ___ of my ___”
• Introduction problems — “A introduces B as…”
• Multi-clue puzzles — 4-5 clues to build a complete family tree, then answer a specific question
• Coded relationships — long chains like “son of the wife of the brother of…”
• Negative information — “A is not the brother of B” (elimination)

Practice Problems

Problem 1: A is the father of B. B is the sister of C. C is the husband of D. E is the daughter of D. How is E related to A?

Problem 2: Pointing to a man in a photograph, a woman says “His mother is the only daughter of my mother.” How is the woman related to the man?

Problem 3: In a family, there are six members A, B, C, D, E, and F. A and B are a married couple. A is the father. C is the only son of A. D is the daughter of B. E is the brother of D. F is the mother-in-law of B. How is F related to C?

Answers

Problem 1: A is father of B and C (siblings). C is married to D. E is daughter of D (and C). So E is the child of A’s son → E is A’s granddaughter.

Problem 2: “The only daughter of my mother” = the woman herself (she is her mother’s only daughter). So the man’s mother is the woman herself. The woman is the man’s mother.

Problem 3: B is married to A (father). F is B’s mother-in-law, which means F is A’s mother. C is A’s son, so F is C’s grandmother.