Logical Reasoning
Learning Objectives
- Understand the fundamental concepts of Logical Reasoning
- Apply key formulas and techniques to solve problems
- Practice with exam-level questions to build speed and accuracy
Key Concepts
What is Logical Reasoning?
Logical Reasoning in GATE General Aptitude tests your ability to identify patterns, analyse relationships, and draw valid conclusions. Topics include analogies, syllogisms, puzzles, blood relations, direction sense, and number/letter series. GATE typically has 2-3 logical reasoning questions in the aptitude section.
Key Concepts
1. Analogies: Relationships include synonym/antonym, cause-effect, part-whole, worker-tool, product-material, animal-young one, degree of intensity. For letter analogies, use positional values (A=1 to Z=26). Number analogies use arithmetic operations.
2. Syllogisms: Statement types: All A are B (circle A inside B), No A is B (separate circles), Some A are B (overlapping circles), Some A are not B (partial overlap). A conclusion follows only if true in ALL possible Venn diagrams.
3. Blood Relations: Build a family tree step by step. Key: 'son of' or 'daughter of' indicates parent-child relationship. 'Brother/sister of' indicates sibling relationship. 'Husband/wife of' indicates marital relationship.
4. Direction Sense: Track movement step by step using a grid. Draw arrows for each movement. Right turn = +90° (clockwise from current direction). Left turn = -90° (anticlockwise). Use Pythagoras for net displacement.
5. Number & Letter Series: Number series: check differences, ratios, squares/cubes, alternating patterns, Fibonacci. Letter series: check positional value differences — often involves consistent addition/subtraction or a pattern of operations.
Solved Examples
a) Building b) Design c) Construction d) Site
a) Brother b) Son c) Cousin d) Nephew
a) 42 b) 44 c) 48 d) 49
Shortcut Techniques
- For syllogisms in GATE, the Venn diagram method is most reliable. Draw all possible configurations before checking conclusions.
- In blood relations, carefully track gender-specific terms (only 'mother' and 'sister' indicate female; 'father', 'brother', 'son' indicate male).
- For series questions, examine differences first — if differences are constant or follow a pattern, you've found it. If not, check ratios or alternate terms.
- In direction problems, draw a diagram for each movement — mental tracking often leads to errors in multi-step problems.
- For analogy questions, identify the exact relationship in the first pair before checking options — multiple options may have partial similarity.
Advanced Applications
Modern exams feature questions combining multiple quantitative concepts. Master these by practicing previous year papers.
Shortcut Methods
Percentages: Use fraction table (12.5%=1/8, 20%=1/5, 25%=1/4). SI/CI: For 2 years, CI-SI = P(r/100)^2. Time Work: Use LCM of time periods. Average Speed: 2ab/(a+b) for equal distances.
Advanced Applications
Modern exams feature questions combining multiple quantitative concepts. Master these by practicing previous year papers.
Shortcut Methods
Percentages: Use fraction table (12.5%=1/8, 20%=1/5, 25%=1/4). SI/CI: For 2 years, CI-SI = P(r/100)^2. Time Work: Use LCM of time periods. Average Speed: 2ab/(a+b) for equal distances.
Advanced Applications
Modern exams feature questions combining multiple quantitative concepts. Master these by practicing previous year papers.
Shortcut Methods
Percentages: Use fraction table (12.5%=1/8, 20%=1/5, 25%=1/4). SI/CI: For 2 years, CI-SI = P(r/100)^2. Time Work: Use LCM of time periods. Average Speed: 2ab/(a+b) for equal distances.
Advanced Applications
Modern exams feature questions combining multiple quantitative concepts. Master these by practicing previous year papers.
Shortcut Methods
Percentages: Use fraction table (12.5%=1/8, 20%=1/5, 25%=1/4). SI/CI: For 2 years, CI-SI = P(r/100)^2. Time Work: Use LCM of time periods. Average Speed: 2ab/(a+b) for equal distances.