Negative Constraint
Negative Constraint problems provide statements that exclude certain relationships (e.g., 'A is not the father of B'). These exclusions, combined with positive statements, help narrow down possibilities and deduce the correct relationship.
What You'll Learn
Introduction to Negative Constraint
Negative Constraint problems provide statements that exclude certain relationships (e.g., 'A is not the father of B'). These exclusions, combined with positive statements, help narrow down possibilities and deduce the correct relationship.
Prerequisites
How to Solve Negative Constraint Problems
Step 1: List all positive relationship statements
Step 2: List all negative constraints (what is NOT true)
Step 3: Build possible family trees based on positive statements
Step 4: Apply negative constraints to eliminate impossible configurations
Step 5: If multiple possibilities remain, note that the answer may be ambiguous
Step 6: For the specific relationship in question, check if it is forced by the constraints
Step 7: Answer based on what remains possible after applying all constraints
Example Problem
Example: 'A and B are siblings. A is not the brother of B.' What can we conclude? Solution: Step 1: Positive: A and B are siblings → share parents Step 2: Negative: A is not the brother of B → A is not male Step 3: Therefore, A must be female Step 4: A is sister of B Answer: A is the sister of B
Pro Tips & Tricks
- 'Not brother' means the person is either sister or not sibling at all
- 'Not father' means the person could be mother, grandfather, uncle, etc.
- Combine negative constraints with positive ones to force unique conclusions
- If a negative constraint eliminates all possibilities, the data is inconsistent
- Use a table to track which relationships are possible for each person pair
- Negative constraints are most powerful when combined with uniqueness clues ('only son')
Shortcut Methods to Solve Faster
Common Mistakes to Avoid
Practice Worksheets
Practice makes perfect! Work through these worksheets to master Negative Constraint. Each worksheet contains 20 questions with detailed explanations. Start from Worksheet 1 and progress through increasing difficulty levels.
Exam Importance
Negative Constraint is an important topic for various competitive exams. Here's how frequently it appears:
Ready to Master Negative Constraint?
Start with Worksheet 1 and work your way up to expert level! Each worksheet includes: