Logical Reasoning: Constraints, Deduction, and Puzzles
What Logical Reasoning tests
This section checks whether you can hold a set of constraints in mind and derive only what is forced. Recurring types are linear and circular arrangements, grouping and distribution puzzles, blood relations, direction sense, syllogisms, coding–decoding, number and letter series, and data sufficiency.
Core rules
- Draw the arrangement physically. Fix definite positions first, then branch on the two-way cases.
- In blood relations, convert each sentence into a directed link (A is father of B) before answering.
- Syllogisms: 'All A are B' converts to 'Some B are A'; 'Some A are B' is reversible; 'No A is B' is reversible.
- In data sufficiency, decide whether the data is sufficient - do not waste time solving for the value.
Worked example
Statements: All pens are books. Some books are red. Conclusions: (I) Some pens are red. (II) Some books are pens.
'All pens are books' places the pens set inside the books set. The red books may lie entirely outside the pens region, so conclusion I is not forced. Conversion of 'All pens are books' gives 'Some books are pens', so conclusion II follows. Answer: only II follows.
Traps
Reading 'some' as 'some but not all'. Assuming a unique arrangement when two remain possible. Importing real-world knowledge beyond definitional facts (a father is male is fine; a doctor is male is not). Answering from a partial diagram before checking the remaining clues. Negative marking applies to MCQ items, so abandon an unfinished puzzle rather than guess blindly.