2.3 Blood Relations

2.3 Blood Relations

Exam Focus: Blood Relations contributes 2 to 3 direct marks in SBI Clerk Prelims—often serving as a vital qualifying anchor—and integrates directly into complex seating puzzles and coded logic representations in Mains.

The Standard Symbolic Family Tree Notation

In high-speed competitive examinations, attempting to solve blood relations mentally leads to cognitive overload and generational confusion. Candidates must build a consistent, automatic graphical notation system.

The Universal Diagramming Conventions

Essential Relational Terminology & Distinctions

• Paternal vs. Maternal Lineage:
  • Paternal: Related through the father (e.g., Paternal Uncle = Father's brother; Paternal Grandmother = Father's mother).
  • Maternal: Related through the mother (e.g., Maternal Uncle = Mother's brother; Maternal Grandfather = Mother's father).
  • Exam Convention: If a question simply states "Uncle" or "Aunt" without specifying, it can be either side unless constrained by options; however, SBI Clerk increasingly specifies maternal or paternal to test precision.
• In-Law Relationships:
  • Brother-in-law: (1) Spouse's brother, OR (2) Sister's husband, OR (3) Wife's sister's husband.
  • Sister-in-law: (1) Spouse's sister, OR (2) Brother's wife, OR (3) Husband's brother's wife.
• Generational Offspring:
  • Nephew: Brother's or sister's son.
  • Niece: Brother's or sister's daughter.
  • First Cousin: Child of one's uncle or aunt (strictly gender-neutral; a cousin is never an "in-law").

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Single-Statement Narratives ("Pointing to a Photograph / Person")

Conversational questions follow a classic phrasing: "Pointing to a photograph of a man, Neha said..."

The Reverse Decoding Protocol

Instead of reading from beginning to end, decompose the sentence from right to left, anchoring on the possessive pronoun "my":

Worked Example 1:

"Pointing to a man in a photograph, a woman said, 'His mother's only daughter is my mother.' How is the woman related to the man in the photograph?"

1. Locate the Speaker's Anchor: The speaker is a woman ("my").
2. Break Down the Statement:
   • Phrase: "His mother's only daughter is my mother."
   • Sub-clause A: "His mother's only daughter"
     • The man in the photograph has a mother.
     • The mother has an "only daughter".
     • The only daughter of the man's mother must be the man's sister.
   • Sub-clause B: "...is my mother"
     • Therefore, the man's sister is the woman's mother.
3. Synthesize the Relationship:
   • The woman's mother is the man's sister.
   • Therefore, the man is the woman's maternal uncle.
   • The question asks: "How is the woman related to the man?"
   • Result: The woman is his Niece.

The "Only Son / Only Daughter" Trap:

• "Only son of my father" $\implies$ If the speaker is male, it is the speaker himself. If the speaker is female, it is her brother.
• "Only child of my father" $\implies$ Always the speaker, regardless of gender.
• Do not assume an "only son" has no siblings; he may have multiple sisters!

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Multi-Generation Family Tree Puzzles (Prelims 3-Question Sets)

In Prelims, 3-question sets present a multi-sentence narrative detailing a family across 2 or 3 generations.

Comprehensive Worked Problem

Scenario: "A family consists of 8 members: P, Q, R, S, T, U, V, and W across three generations. There are exactly three married couples. P is married to R. P is the father of T. T is married to Q. T is the brother of U. U is married to S. S is the son-in-law of R. V is the son of S. W is the daughter of U. Q has no children."

Step-by-Step Construction & Deduction

1. Establish Generation 1 (Foundational Couple):

   • Clue: "P is married to R. P is the father of T."
   • $P$ is male ($P+$). Since $P$ is married to $R$, $R$ must be female ($R-$).
   • Couple 1: $P(+) = R(-)$ (Generation 1).

2. Establish Generation 2 (Offspring and Spouses):

   • Clue: "P is the father of T. T is the brother of U."
   • Both $T$ and $U$ are the children of $P$ and $R$.
   • $T$ is male ($T+$). $T$ is married to $Q$ $\implies Q$ is female ($Q-$).
   • Couple 2: $T(+) = Q(-)$.
   • Clue: "U is married to S. S is the son-in-law of R."
   • Since $U$ is the daughter of $R$, $U$ is female ($U-$), and her husband $S$ is male ($S+$).
   • Couple 3: $S(+) = U(-)$.
   • Check married couple count: Exactly 3 couples ($P=R$, $T=Q$, $S=U$). All accounted for.

3. Establish Generation 3 (Grandchildren):

   • Clue: "V is the son of S. W is the daughter of U. Q has no children."
   • Since $S$ and $U$ are married, $V$ and $W$ are their children.
   • $V$ is male ($V+$); $W$ is female ($W-$).
   • They are brother and sister ($V+ — W-$).

Structural Family Tree Representation

Generation 1:          [ P (+) ] ========== [ R (-) ]
                                      |
                     -----------------------------------
                     |                                 |
Generation 2:    [ T (+) ] === [ Q (-) ]           [ S (+) ] === [ U (-) ]
                 (No children)                                 |
                                                   -------------------------
                                                   |                       |
Generation 3:                                  [ V (+) ] —————————————— [ W (-) ]

Direct Deductions from the Constructed Tree

• How is Q related to U? $Q$ is married to $U$'s brother $T$. Therefore, $Q$ is the sister-in-law of $U$.
• How is R related to W? $R$ is the mother of $W$'s mother ($U$). Therefore, $R$ is the maternal grandmother of $W$.
• How is T related to V? $T$ is the brother of $V$'s mother ($U$). Therefore, $T$ is the maternal uncle of $V$.

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Mains Coded Blood Relations: Fast-Track Elimination

In SBI Clerk Mains, blood relations are expressed as symbolic mathematical equations. Drawing the full tree for every answer choice takes over 3 minutes. Expert candidates use the Two-Tier Elimination Technique.

The Operational Code Key

• $A + B \implies A$ is the father of $B$ ($+1$ generation, Male)
• $A - B \implies A$ is the mother of $B$ ($+1$ generation, Female)
• $A \times B \implies A$ is the brother of $B$ ($0$ generation, Male)
• $A \div B \implies A$ is the sister of $B$ ($0$ generation, Female)
• $A = B \implies A$ is the wife of $B$ ($0$ generation, Female)

Tier 1: Gender Verification

If the question asks "Which of the following expressions indicates that M is the sister of K?", then $M$ must be female.

• If an option ends with $M$ without any defining operator after it (e.g., $... \times M$), $M$'s gender is often indeterminate $\implies$ Eliminate immediately.
• If an expression assigns a male operator directly to $M$ (e.g., $M + ...$ or $M \times ...$), $M$ is male $\implies$ Eliminate immediately.

Tier 2: Generational Gap Calculation

Assign an algebraic generational value to each operator:

• Parent Operators (Father $+$, Mother $-$): $+1$
• Sibling / Spouse Operators (Brother $\times$, Sister $\div$, Wife $=$): $0$
• Child Operators (Son, Daughter): $-1$

Sum the values along the path from source to target. If the required relationship is "Grandmother", the net sum must equal $+2$.

Worked Example:

Evaluate the expression: $\mathbf{M - K \times T + N}$

1. Path from $M$ to $N$:
   • $M - K$: $M$ is mother of $K$ (Gender of $M$: Female; Gap: $+1$)
   • $K \times T$: $K$ is brother of $T$ (Gap: $0$)
   • $T + N$: $T$ is father of $N$ (Gap: $+1$)
2. Net Generational Gap: $+1 + 0 + 1 = \mathbf{+2}$.
3. Relationship Synthesis: $M$ is the mother of $T$ (since $K$ and $T$ are brothers), and $T$ is the father of $N$.
4. Result: $M$ is the paternal grandmother of $N$.

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Critical Traps and Guidelines

1. The Name-Gender Trap: In SBI Clerk, a name like "Kiran", "Suman", or "Sunny" does not determine gender. If the text says "Kiran is the child of Deepak", Kiran's gender is unknown until a pronoun ("he"/"she") is explicitly stated.
2. Sibling-in-Law Ambiguity: Always verify whether "brother-in-law" refers to spouse's brother or sister's husband before finalizing seating coordinates.
3. Cousin Misclassification: First cousins share grandparents but belong to the same generation ($0$ gap). They can never be nieces, nephews, or siblings.
4. Directional Reversal in Coded Statements: Beware of trick keys where $A * B$ means "B is the father of A" instead of the standard "A is the father of B". Always check the order of operands in the instructions.