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Aptitude · Lesson 9 of 9

Logical reasoning

Coding-decoding, blood relations, direction sense and syllogisms.

Coding–decoding

Find the rule: letter shifts (+1, −2), reversal, or position numbers (A=1 … Z=26). Write the alphabet with positions once at the start of the test.

Example: If KOCHI is coded as LPDIJ, how is PARK coded?

  1. Each letter moves +1: K→L, O→P, C→D, H→I, I→J.
  2. P→Q, A→B, R→S, K→L.

Answer: QBSL

Blood relations

Draw a quick family tree: + for male, − for female, horizontal lines for siblings/spouses, vertical lines for generations.

Example: Pointing to a photo, Anil says, “She is the daughter of my grandfather's only son.” How is the girl related to Anil?

  1. Grandfather's only son = Anil's father.
  2. Daughter of Anil's father = Anil's sister.

Answer: Sister

Direction sense

Example: Meera walks 6 km north, turns right and walks 8 km. How far is she from the start?

  1. North then right = east: legs of 6 and 8 at right angles.
  2. Distance = √(6² + 8²) = √100.

Answer: 10 km, towards the north-east

Syllogisms

Draw Venn circles for each statement and accept a conclusion only if it is true in every possible diagram. “All A are B” and “Some B are C” does not prove “Some A are C”.

Key points

  • Write the alphabet positions before you start.
  • Draw family trees and direction sketches.
  • Syllogism conclusions must hold in every Venn diagram.

Quick check

Facing north, you turn right, then right again, then left. Which way are you facing?

Practice task

If in a code DELHI is written as 73541 and CALCUTTA as 82589662, how is CALICUT written? (Each letter maps to a fixed digit.)

Show answer

From the codes: C=8, A=2, L=5, I=1, U=9, T=6. CALICUT = 8 2 5 1 8 9 6 → 8251896.

Interview corner

How do you approach a long seating-arrangement puzzle?

Fix the most definite clue first, draw positions, place certain items, branch into cases for uncertain clues, and eliminate contradictions.

Statements: All pens are books. Some books are bags. Conclusion: Some pens are bags. Valid?

Not necessarily — the bags may overlap only the books that are not pens, so the conclusion doesn't follow.

Original lesson written by the InfoparkDaily team · © 2026 InfoparkDaily · Free to learn — no paid course or subscription.