family_binary_relations

Family Binary Relations problems combine binary logic with family relationships (father, mother, son, daughter, etc.). Persons make statements about family relationships and their truth-telling types. These puzzles test both logical deduction and understanding of familial terms.

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200+Practice Questions
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Introduction to family_binary_relations

Family Binary Relations problems combine binary logic with family relationships (father, mother, son, daughter, etc.). Persons make statements about family relationships and their truth-telling types. These puzzles test both logical deduction and understanding of familial terms.

Prerequisites

Truth-teller/Liar logic Family relationship terms (mother, father, brother, sister) Gender inference Case analysis
Why This Matters: These puzzles appear in moderate to advanced reasoning sections. Expect 1-2 questions in SSC CGL and Banking PO mains.

How to Solve family_binary_relations Problems

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Step 1: List all family members and their relationships as given.

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Step 2: Translate each statement into a logical condition about types and relationships.

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Step 3: Use case analysis, assuming a key person is a truth-teller or liar.

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Step 4: Track the gender of persons when needed (e.g., 'father' implies male).

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Step 5: Use the constant nature of family relationships (e.g., if X is father of Y, then X is male and Y is child).

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Step 6: Eliminate inconsistent assignments.

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Step 7: Answer the question (e.g., 'Who is the truth-teller?').

Example Problem

Example: Father says: 'My wife tells the truth.' Mother says: 'My son is a liar.' Son says: 'My father is a liar.' Determine the truth-tellers. Solution: Step 1: Let F=Father, M=Mother, S=Son. Step 2: Assume F is truth-teller. Then 'M is truth-teller' is true → M is truth-teller. M says 'S is liar' is true → S is liar. S(liar) says 'F is liar' is false → F is truth-teller (consistent). This gives F=T, M=T, S=L. Step 3: Assume F is liar. Then 'M is truth-teller' is false → M is liar. M says 'S is liar' is false → S is truth-teller. S(T) says 'F is liar' is true → F is liar (consistent). This gives F=L, M=L, S=T. Step 4: Both assignments are consistent! The puzzle may need an additional constraint to be unique. Answer: Two possible solutions: (F=T, M=T, S=L) or (F=L, M=L, S=T).

Pro Tips & Tricks

  • Draw a small family tree to visualize relationships.
  • Gender is often implied by the relationship term (father, mother, son, daughter).
  • The statement 'My wife' implies the speaker is male.
  • The statement 'My son' implies the speaker is a parent (could be father or mother, but gender is known from 'my' if speaker's gender is known).
  • Use the constant difference in age/relationship to resolve ambiguities.

Shortcut Methods to Solve Faster

If father and son accuse each other of lying, they cannot both be truth-tellers or both liars; one must be T and the other L.
A mother calling her son a liar and the son calling his father a liar creates a cyclic dependency.

Common Mistakes to Avoid

Assuming gender incorrectly (e.g., 'parent' could be father or mother).
Forgetting that family relationships are bidirectional (if X is father of Y, then Y is child of X).
Not tracking the implications of a statement about a relationship.

Exam Importance

family_binary_relations is an important topic for various competitive exams. Here's how frequently it appears:

SSC CGL
1-2 questions
BANKING PO
1-2 questions
RAILWAYS RRB
1-2 questions
CAT
0-1 questions
INSURANCE
1-2 questions

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Start with Worksheet 1 and work your way up to expert level! Each worksheet includes:

20 practice questions
Detailed solutions
Step-by-step explanations
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