Analytical & Logical Reasoning

Syllabus Unit: General Aptitude

Why it matters

Chapter overview

Analytical and logical reasoning questions test structured deduction under time pressure — decoding a hidden rule in a number/letter series, applying syllogism validity rules to All/Some/No statements, placing entities correctly in a seating arrangement from partial clues, and tracking blood relations or compass directions through several linked statements.

General Aptitude & Mathematics General Aptitude 15% weightage

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List given terms/letters in order

Compute the difference or ratio between consecutive items

Confirm the rule holds for every pair, not just the first

Apply the confirmed rule to find the missing term

1Series & Coding-Decoding

Every number/letter series hides one consistent rule — find the operation between consecutive terms, not the terms themselves; coding-decoding is the identical idea applied to a fixed letter-shift or substitution rule.

Learning Objectives

Identify common series patterns: arithmetic, geometric, and mixed operation series.
Recognise a two-stream alternating series where odd and even positions follow different rules.
Apply letter-position coding (A=1...Z=26) to solve shift-based coding-decoding problems.
Decode a substitution scheme by testing the same rule consistently across every letter of a known example.

Key Terms

Arithmetic/Geometric SeriesA series with a constant difference (arithmetic) or constant ratio (geometric) between consecutive terms.

Alternating (Two-Stream) SeriesA series that interleaves two independent sub-series, one at odd positions and one at even positions.

Letter-Shift CodingA coding scheme where every letter of a word is shifted a fixed number of places in the alphabet.

Letter-to-Number CodingThe convention A=1, B=2, ..., Z=26, used to convert letters into numbers for coding-decoding puzzles.

Every series hides exactly one consistent rule between consecutive terms — the entire skill is testing candidate rules against every pair of terms, not just the first.

Common series rules

Arithmetic — constant difference (2, 5, 8, 11, ...: +3 each time).
Geometric — constant ratio (3, 6, 12, 24, ...: ×2 each time).
Mixed operation — combined rule (3, 7, 15, 31, 63, ...: ×2+1 each time).
Squares/cubes — (1, 4, 9, 16, 25: n²) or (1, 8, 27, 64: n³).

Exam TipCompute the differences between consecutive terms first; if those differences are themselves in an arithmetic/geometric pattern, the series is a second-order series — a common GATE escalation of the basic idea.

Two-stream series and coding-decoding

Some series interleave two independent rules — split the series into two sub-series by position before searching for a pattern. Coding-decoding works by letter position: A=1, B=2, ..., Z=26; 'CAT → DBU' shifts every letter forward by 1 (C→D, A→B, T→U).

Common MistakeVerify the rule against every letter of the given example, not just the first — a rule that works for letter 1 but not letter 2 is not the actual rule (some codes shift consonants and vowels differently).