Blood Relations: Complete Master Guide for UPSC/MPSC CSAT (English)

Introduction to Blood Relations in CSAT

Blood Relations is a crucial topic in the Logical Reasoning section of the CSAT for UPSC and MPSC. This topic tests a candidate’s cognitive ability to map out familial structures, decipher complex relational statements, and arrive at logical conclusions regarding how individuals are connected to one another. Despite appearing convoluted due to the twisted phrasing of the questions, Blood Relations can be one of the most scoring sections if approached with a structured methodology.

In competitive exams, questions generally fall into three categories: narrative or dialogue-based (where one person points to another and makes a statement), puzzle-based (involving a family tree with multiple generations), and coded relations (where mathematical symbols represent relationships). A strong grasp of standard terminology (like niece, nephew, sibling, in-laws) and a systematic visual representation are the keys to mastering this topic.

Core Concepts, Terminology, and Tricks

1. Common Terminologies

Before diving into problems, one must be absolutely clear about English relationship terms:

• Siblings: Brothers and sisters.
• Spouse: Husband or wife.
• Paternal: Relationships on the father’s side (e.g., Paternal Uncle = Father’s brother).
• Maternal: Relationships on the mother’s side (e.g., Maternal Uncle = Mother’s brother).
• Nephew/Niece: Brother’s or sister’s son (Nephew) / daughter (Niece).
• Cousin: Child of an uncle or aunt (Note: “Cousin brother” or “Cousin sister” is grammatically incorrect in standard English logic; they are simply cousins).
• In-laws: Relations created by marriage (e.g., Father-in-law = Spouse’s father, Brother-in-law = Spouse’s brother or sister’s husband).

2. Family Tree Construction (The Trick)

The most foolproof way to solve blood relation problems is by drawing a Family Tree using standard symbols:

• Gender: Use a square/box (□) or ‘+’ for a Male, and a circle (○) or ‘-‘ for a Female.
• Generations: Use a vertical line (|) to connect different generations (e.g., Father to Son).
• Siblings: Use a single horizontal line (—) to connect brothers and sisters.
• Marriage: Use a double horizontal line (=) or a plus sign between symbols to show a married couple.

3. Decoding “Pointing to…” Questions

For questions like “Pointing to a photograph, A said…”, the trick is to break the sentence down and solve it in reverse order. Always start from the word “My” (which refers to the speaker) and trace the relations backwards.

Solved Examples

Example 1: Dialogue/Pointing Type

Question: Pointing to a photograph of a boy, Suresh said, “He is the son of the only son of my mother.” How is Suresh related to that boy?

Solution:
Step 1: Identify the speaker. The speaker is Suresh.
Step 2: Start from “my” in the sentence. “My mother” = Suresh’s mother.
Step 3: “Only son of my mother”. Since Suresh is a male (generally assumed by name unless specified, but here it fits perfectly), the only son of Suresh’s mother is Suresh himself.
Step 4: Now read the first part: “He is the son of… (Suresh)”.
Therefore, the boy is Suresh’s son, making Suresh the father of the boy.
Answer: Father.

Example 2: Puzzle Based (Family Tree)

Question: 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?
a) B is the brother of A.
b) B is the son of D.
c) A is the brother of C.
d) C is the brother of A.

Solution:
Let’s construct the family tree:
A (+) — B (+). [A and B are brothers].
B (+) — C (?). [B is brother of C, but C’s gender is unknown].
D (+) is the father of A. So D is above A, B, and C.
Now check the options:
a) B is the brother of A – True (since both are +).
b) B is the son of D – True.
c) A is the brother of C – True.
d) C is the brother of A – We don’t know if C is male or female. C could be a sister. So this cannot be definitely true.
Answer: d) C is the brother of A.

Example 3: Coded Relations

Question: If P + Q means P is the husband of Q; P / Q means P is the sister of Q; P * Q means P is the son of Q. How is D related to A in D * B + C / A?

Solution:
Break down the expression D * B + C / A from left to right:
1. D * B → D is the son of B. (D is +, B is above D).
2. B + C → B is the husband of C. (B is +, C is -, they are married. So C is the mother of D).
3. C / A → C is the sister of A. (A is C’s sibling).
Question: How is D related to A?
D is the son of C, and C is the sister of A. Therefore, D is the son of A’s sister.
The son of one’s sister is a nephew.
Answer: Nephew.

Pro-Tips to Avoid Common Mistakes

• Never assume gender based on names: Unless explicitly stated or implied by words like “only son” or “husband”, do not assume ‘Kiran’ or ‘Sonu’ is male or female.
• “Only” is a keyword: Pay extreme attention to the word “only”. “Only son” means there are no other sons, but there could be daughters. “Only child” means no other sons or daughters.
• Read the final question carefully: “How is A related to B?” is completely different from “How is B related to A?”. If A is the uncle of B, B is the nephew/niece of A.
• Draw the tree: Do not try to solve puzzle-based questions entirely in your head. Drawing the tree takes 10 seconds but guarantees 100% accuracy.

Practice Questions

Q1. Pointing to a woman, a man says, “She is the only daughter of my wife’s grandfather’s only child.” How is the woman related to the man?

A) Mother
B) Sister
C) Wife
D) Daughter

Q2. A and B are young ones of C. If C is the father of A but B is not the son of C. How are B and C related?

A) Niece and Uncle
B) Daughter and Father
C) Sister and Brother
D) None of these

Q3. If A is the mother of D, B is not the son of C, C is the father of D, D is the sister of B, then how is A related to B?

A) Mother
B) Brother
C) Step-mother
D) Sister

Answers:

1. C (Wife’s grandfather’s only child = Wife’s parent. Only daughter of wife’s parent = the wife herself.)
2. B (If B is the young one of C but not the son, B must be the daughter. C is the father.)
3. A (A is mother of D. C is father of D. So A and C are married. D is sister of B, so A and C are parents of B. Therefore, A is the mother of B.)