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Logical reasoning
Reasoning Ability
Useful for: OSSC RHT — Regular High School Teacher, OSEPA Primary Teacher / JT Category-I, OSEPA Upper Primary — Arts, OSEPA Upper Primary — Science, OSSSC Govt Physical Education Teacher (PET), OSSSC Govt TGT Arts, OSSSC Govt TGT Science — CBZ, OSSSC Govt TGT Science — PCM
Overview
Logical reasoning includes syllogisms, series, coding, arrangements, blood relations, directions and statement-based logic.
Key points
- Syllogisms: use Venn diagrams; accept only certain conclusions.
- Series: check differences, ratios, squares and alternate patterns.
- Arrangements: place fixed clues first, then branch.
- Directions: keep net (x, y) displacement.
- Blood relations: draw a family tree with generations.
- Statement–assumption: use the negation test.
Explanation
- Read every condition carefully; one missed clue changes the arrangement.
- Use elimination from options.
- Some items mix numeracy and logic.
- Keep diagrams tidy.
Step by step
- Identify the concept, method or fact asked.
- Recall the definition, thinker, year or rule.
- Apply it and eliminate extreme or mismatched options.
Examples
- All A are B; some B are C → "some A are C" does not follow.
- Series 2, 6, 12, 20, 30 → next 42 (differences 4, 6, 8, 10, 12).
- Walk 3 km north and 4 km east → 5 km north-east of the start.
Traps and advanced points
- Trap: Accepting possible conclusions as certain.
- Trap: Missing alternate series.
- Trap: Skipping a clue.
Quick revision
- Venn for syllogisms.
- Differences then ratios.
- Diagram every arrangement.
Practice MCQs
All A are B; some B are C. Does "some A are C" follow?
- Always
- Yes
- No
- Only if all B are C
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Answer: (c) No. The overlap of B and C may not include A.
Next number: 2, 6, 12, 20, 30, ?
- 44
- 36
- 40
- 42
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Answer: (d) 42. Differences 4, 6, 8, 10, 12.
A person walks 3 km north and then 4 km east. Distance from the start —
- 7 km
- 5 km
- 1 km
- 12 km
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Answer: (b) 5 km. √(9 + 16) = 5.
In arrangement puzzles, start with —
- fixed clues
- negative clues
- the last clue
- guesses
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Answer: (a) fixed clues. Definite clues fix positions.
The negation test is used for —
- spelling
- statement–assumption questions
- number series
- mensuration
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Answer: (b) statement–assumption questions. If negating the assumption breaks the argument, it is assumed.
In blood relation questions, the best tool is a —
- timeline of dates
- map
- family tree with generations
- pie chart
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Answer: (c) family tree with generations. Trees show relations clearly.
All cats are animals; all animals are living. Conclusion: all cats are living.
- Follows
- Does not follow
- Uncertain
- Only some cats
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Answer: (a) Follows. All + all = all.
Some books are pens; no pen is a bag. Which follows?
- No book is a bag
- All books are bags
- Some bags are pens
- Some books are not bags
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Answer: (d) Some books are not bags. The books that are pens cannot be bags.
Next term: 1, 4, 9, 16, ?
- 25
- 24
- 36
- 20
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Answer: (a) 25. Squares: 5² = 25.
A clock shows 3:00. The angle between the hands is —
- 60°
- 90°
- 120°
- 180°
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Answer: (b) 90°. |30 × 3 − 5.5 × 0| = 90°.
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