Logical Reasoning: Series, Coding and Arrangement
Domain 2, Logical Reasoning, tests pattern recognition and constraint-based reasoning: number and letter series, coding–decoding, direction sense, seating/arrangement and blood relations. The exam rewards a written abstraction of the rule before calculating.
Core rules
- In a number series, test first differences, then second differences, ratios, alternating terms and squares/cubes. A single series may combine two rules.
- In coding–decoding, map letters by position (A=1 ... Z=26) and record the shift for each letter; shifts may alternate or reverse.
- For direction sense, draw axes and track net displacement; left/right turns are relative to the current facing direction.
- In linear seating, fix one certain position and place “immediate left/right” neighbours before applying “somewhere between” clues.
Worked example
Find the next term: 2, 6, 12, 20, 30, ?. The first differences are 4, 6, 8, 10; these increase by 2, so the next difference is 12 and the next term is 30 + 12 = 42. Equivalently, the terms are n(n+1) for n = 1,2,3,4,5, so the sixth is 6×7 = 42. For a code, if CAT is written DBU by shifting every letter one place forward, then DOG becomes EPH.
Traps
Do not assume the first visible difference is the rule; check at least two steps. In seating, “left” of a person facing south is the observer’s right. In blood relations, do not assign gender from a relation word unless the clue fixes it. For coding, preserve letter case and wrap-around only when stated.