Reasoning
What this domain tests
Reasoning carries 35 marks in the prelims and mixes puzzles and seating arrangements with syllogism, coding-decoding, blood relations, direction sense, inequality, alphanumeric series and data sufficiency.
Core rules
- Puzzles and seating - draw the arrangement; fix certain facts first, keep two or three possible frames when a clue is ambiguous, and eliminate frames as clues confirm.
- Syllogism - think in Venn diagrams. "All A are B" plus "Some B are C" proves nothing about A and C. Only a conclusion true in every possible diagram follows.
- Inequality - chain the symbols; A > B ≥ C gives A > C, but a strict symbol hidden in the chain can make a stated conclusion false.
- Coding-decoding - find the letter-position shift per word, or the rule that reverses and then shifts.
- Blood relations - draw a family tree with a consistent symbol for male, female and marriage; never hold the tree in your head.
- Direction sense - plot with north up and use Pythagoras for the shortest distance.
Worked example
A man walks 4 km north, turns right and walks 3 km, turns right again and walks 4 km. Plotting: (0,0) → (0,4) → (3,4) → (3,0). He ends 3 km east of the start and is facing south. If asked for the shortest distance back to the starting point, it is 3 km.
Traps
Accepting a "some" conclusion because it looks plausible; missing that an either-or conclusion requires both possibilities to fail; drawing a north-facing row anticlockwise so that left becomes east instead of west; forgetting that floor puzzles usually number from the floor stated in the question.