Reasoning Ability: Series, Syllogism and Puzzles
Reasoning Ability checks structured thinking: number and letter series, coding-decoding, syllogism, seating and puzzles, blood relations, inequalities and direction sense. The exam rewards a fixed method for each question type rather than intuition.
Method rules
- Number series: test differences first, then ratios, then squares or cubes with a constant offset, then alternating or two interleaved series.
- Coding-decoding: write A=1 to Z=26, verify the shift on the first pair, then apply it to the whole word; watch for reversal.
- Syllogism: draw the minimum-overlap Venn diagram. A conclusion is valid only if it is true in every possible diagram; a possibility conclusion needs just one valid diagram.
- Circular seating: fix the most constrained person first, mark facing direction with arrows, and interpret left and right relative to the facing direction.
- Blood relations: build a tree with gender symbols; do not solve it mentally.
Worked example
Series: 3, 8, 15, 24, 35, ?
- Differences: 5, 7, 9, 11 - consecutive odd numbers rising by 2.
- Next difference = 13, so the answer is 35 + 13 = 48.
- Cross-check: each term is n² − 1 for n = 2 to 6, so the next is 7² − 1 = 48. Two independent methods agreeing confirms the term without guessing.
Traps
- Reversing left and right when people face the centre versus face outward.
- Treating some A are B as all A are B.
- In inequalities, merging ≥ and > incorrectly while chaining symbols.
- In puzzles, adding a condition that was never stated just to make the arrangement fit.