Logical reasoning: series, coding, arrangements and puzzles

Number and letter series

Look for: differences (and differences of differences), multiplication patterns, squares/cubes (1, 4, 9, 16 / 1, 8, 27), primes, alternating series, and letter positions (A = 1 … Z = 26; also reverse positions: A = 26).

• 2, 6, 12, 20, 30, ? → differences 4, 6, 8, 10, 12 → 42.
• 3, 5, 9, 17, 33, ? → ×2 − 1 → 65.
• B, E, H, K, ? → +3 → N.

Coding-decoding

Find the rule by comparing letters: shifts (+1, −2), reversal, position-based or substitution codes. If CAT = DBU (each letter +1), then DOG = EPH.

Blood relations

Draw a family tree with symbols (+ male, − female, = married, vertical lines for generations). "Pointing to a photo, Raj says, 'He is the son of my grandfather's only son.'" Grandfather's only son = Raj's father; his son = Raj or Raj's brother; since the person is "he" in a photo Raj points at, the answer is usually brother (or Raj himself, depending on the options).

Direction sense

Draw it. North is up; turning right from north faces east. Use Pythagoras for the shortest distance: 3 km north, then 4 km east → 5 km from the start, in the north-east direction.

Seating arrangements and puzzles

1. Draw the layout (a line, a circle facing in or out, floors, a table).
2. Place definite information first.
3. Consider cases for uncertain clues; eliminate contradictions.
4. Keep a clean grid; don't hold it in your head.

Syllogisms

Use Venn diagrams. "All pens are books. Some books are bags." Conclusions: "Some pens are bags": not necessarily (the bags may overlap only with books that aren't pens). "Some books are pens": true (since all pens are books).

Critical reasoning and verbal ability

• Statement and assumption / conclusion / course of action: decide what must be true or what logically follows, not what's merely likely.
• Reading comprehension: read the questions first, then the passage; answer from the passage, not general knowledge.
• Grammar: subject-verb agreement, tenses, articles, prepositions, parallelism.
• Vocabulary: synonyms and antonyms in context; read daily to build it.
• Sentence rearrangement (para jumbles): find the opening sentence (introduces the topic, no pronouns referring back), then link pairs with connectors and pronouns.

A 4-week preparation plan

• Week 1: percentages, profit and loss, ratios, averages, interest + number series. 30 questions a day.
• Week 2: time and work, speed and distance, number systems + coding, blood relations, directions.
• Week 3: permutations, probability, data interpretation + arrangements, puzzles, syllogisms.
• Week 4: verbal ability every day; full-length timed mock tests of your target companies' patterns; review every mistake and keep an error notebook.

Speed tips: learn tables up to 20, squares up to 30 and cubes up to 15; approximate; skip a question that takes over 2 minutes and return later; check negative marking rules before guessing.

Check yourself

• Next term: 1, 4, 10, 22, 46, ?
• If FRIEND = HUMJTK, what is CANDLE?
• A walks 5 km south, turns left and walks 12 km. How far from the start?