CSAT Part 6: Reasoning — Blood Relations, Directions, Puzzles, Exam-Ready Notes

Category: Civil Exams · Series: UPSC CSAT Paper II · Read time: ~8 minutes**

The puzzle family — blood relations, direction sense, seating arrangements and ranking/ordering — looks like it rewards cleverness, but each type has a fixed notation system. Build the notation and the questions become transcription exercises. This note gives the notation, the solving sequence, and the trap register for each type.

Table of Contents

1. Blood Relations: The Tree Notation
2. Coded Blood Relations: Working Backwards
3. Direction Sense: The Coordinate Habit
4. Seating Arrangements: The Anchor-First Method
5. Ranking and Ordering: The Position Formula
6. The Trap Register
7. How Exams Probe This Topic
8. Quick Revision: One-Glance Facts

1. Blood Relations: The Tree Notation

• The symbols. Males as squares/+ , females as circles/− (or write “m”/”f”); horizontal line = marriage; vertical/diagonal line = children of that couple. Write generation levels on separate horizontal rows — most errors are generation collapses.
• The vocabulary decode. “My mother’s only son” can be the speaker himself (decode pronouns from the speaker’s sex); “father’s sister’s husband” = uncle by marriage; “only daughter of” pins a unique person — “only” words are load-bearing, read them twice.
• The solving sequence. Decode the final question first (“how is X related to Y?”), then place Y, then walk the chain from Y outward. Never draw the full tree before knowing what is asked.

2. Coded Blood Relations: Working Backwards

• The format. “A + B means A is the mother of B”; then decode a chain like P + Q − R × S.
• The method. Start from the last relation backwards to the person whose perspective you need; or evaluate pair by pair from the right end, replacing each coded pair with a plain-language relation — the chain collapses like algebra.
• The two checks. (a) Each symbol’s direction: “A + B” is A→B, not B→A; (b) gender is unknown unless stated — an option asserting “nephew” when the chain gives “nibling” (unknown sex) is the designed wrong answer; “cannot be determined” is a real option in this family.

3. Direction Sense: The Coordinate Habit

• The frame. Always draw: North up, right = East. Start with a facing direction arrow, and track turns as arithmetic on the compass (right turn = +90° clockwise).
• The two cases.
  • Journey problems: plot the path on axes; final displacement = √(x² + y²) by Pythagoras; final direction = sign of the net (x, y).
  • Shadow/sun problems: morning sun in the East ⇒ shadows point West; evening reverse. Given a shadow direction + facing, one compass deduction fixes everything.
• Left/right discipline. “His left” depends on current facing — after each turn, re-mark the facing arrow before processing the next instruction. Turning errors, not maths errors, sink these questions.

4. Seating Arrangements: The Anchor-First Method

• The types. Row (single or facing rows), circle — facing centre vs facing outward (the left/right reversal matters), square/hexagon tables.
• The sequence.
  1. Draw the frame and mark slot numbers.
  2. Place the anchor — the person with the most definite info (“V sits third to the left of P” with a fixed position).
  3. Chain the definite clues; keep the conditional clues (“if Q is adjacent to R…”) for last.
  4. When two configurations survive, fork the diagram — test options or remaining clues against each fork rather than guessing.
• Counting rules. “Third to the left of X (facing centre)” = count three seats anti-clockwise from X; facing outward reverses every left/right — write the facing rule at the top of your diagram every time.
• The pairing vocabulary. “Adjacent”, “immediate neighbour”, “exactly between”, “not adjacent to any” — translate to slot arithmetic (±1, ±2) at read time.

5. Ranking and Ordering: The Position Formula

• The formula pair. Total persons = (position from left) + (position from right) − 1. If positions overlap/gap questions arise: gap/overlap = L + R − 1 − Total (positive = overlap, negative = gap of that many between them).
• The wrappers. Heights/weights ordering (“A is taller than B but shorter than C” chains — build a vertical ladder), exam-score ordering, dates/calendar ordering. For ladders, place the extreme (max/min) statements first, then insert the middle statements; “not shorter than” means ≥, another wording trap.
• The intersection type. “How many between X and Y” or “can their positions be determined” — if data gives two possibilities, the answer is often “cannot be determined”; do not force a resolution.

6. The Trap Register

1. Gender assumed — blood relations without stated sex.
2. “Only child/only daughter” missed — uniqueness pins the tree.
3. Facing outward reversal in circular seating.
4. Left/right taken from your perspective instead of the character’s current facing.
5. Morning/evening shadow swapped.
6. Overlap vs gap sign in ranking formula.
7. “Not adjacent” read as “somewhere else” — it excludes exactly ±1, no more.
   Log every practice miss against this register; the register is the revision.

7. How Exams Probe This Topic

• The CSAT record: blood relations (often the coded form), direction sense with displacement Pythagoras, small seating puzzles and ranking appear in most 2014–2025 papers — typically 3–6 questions.
• The drill: notation-first solving — never solve these in the head beyond two links; the diagram is the speed. 20 questions in 20 minutes at 90%+ accuracy is the bar.
• Companion exams: banking PO reasoning (the Banking series, Part 5) runs the identical types at higher volume and difficulty — if you prepare both, do the banking sets as your advanced drill.

8. Quick Revision: One-Glance Facts

• Blood relations. Question-first, generation rows, “only” pins; gender unknown ⇒ cannot-be-determined is live.
• Coded chains. Collapse from the right end pair by pair.
• Directions. Compass frame + facing arrow re-marked each turn; displacement by Pythagoras; shadows reverse morning/evening.
• Seating. Anchor first, definites before conditionals, fork when two survive; outward-facing reverses left/right.
• Ranking. Total = L + R − 1; sign of (L + R − 1 − T) = overlap/gap.

Conclusion. Puzzle questions are notation questions. The tree, the compass, the numbered seats and the position formula turn each type into a transcription task with a diagram doing the memory work. Solve with the diagram even when the answer “looks obvious” — the obvious answers are exactly where the trap register lives — and this block becomes the cleanest reasoning marks in Paper II.

Four Fully-Solved Puzzles (The Notation-Visible)

Puzzle 1 (circular, facing-mixed). Six-friends-around-a-table; A, B, C-face-the-centre; D, E, F-face-out. Clues: A-is-opposite-D; B-is-to-the-immediate-right-of-A; E-is-not-adjacent-to-D. The-solve: fix-A-at-12; the-opposite-D-at-6; B (immediate-right-of-A-facing-centre) = A’s-clockwise = 2-o’clock; E-not-adjacent-to-D → E ≠ 5-and-7 → E-at-4? — the-mixed-facing’s-crux: E-faces-out, so E’s-own-left-and-right-reverse — but the-clue-concerns-adjacency-not-direction → E-at-4-or-2; 2-is-B → E-at-4; the-remaining-C-and-F at-8-and-10. The-lesson: adjacency-is-facing-neutral; “left-of/right-of” is-facing-dependent — the-single-most-tested-distinction.
Puzzle 2 (the floor-stack). Seven-people-on-seven-floors: the-standard-vertical-ladder — the-direct-clues (“P-on-3rd”)-first; the-relative (“Q-two-above-R”)-as-the sliding-pair; the negative (“S-not-on-7”)-as-the eliminator. The-floor-puzzle’s-secret: the top-and-bottom-anchors-constrain-most — place-the-extremes-early.
Puzzle 3 (the scheduling-with-two-variables). Five-courses-on-Monday-to-Friday, each-with-a-professor: the matrix (days × professors)-with-the-course-row — the two-mandatory-pairs (“the-HOD-teaches-the-day-after-the-stats-class”)-placed-first, the fork-at-the pair’s-two-positions-resolved-by-one-question.
Puzzle 4 (the blood-relation-in-the-puzzle). The-combined-type (the family-of-five-with-the professions): the relation-tree-drawn-first (the generations’-rows), the profession-clues-loaded-onto-the-tree (never-the reverse — the-tree’s-structure-constrains-the-professions’-pairs).

The Fork-Audit (The Skill-After-The-Skill)

When-two-configurations-survive-the-clues: do-not-guess-the-diagram — answer-one-question-from-each-fork (the question-that-differs-across-the-forks-identifies-the-live-one-in-30-seconds). The audit’s-discipline-saves-the 2-3-minutes-of-wrong-diagram-work — and-the-mock-log’s-name-for-the-failure (“committed-to-a-fork-without-audit”)-is-one-of-the-top-three-CSAT-reasoning-errors.