Aptitude
Logical Reasoning and Analytical Ability
Logical Reasoning and Analytical Ability — Quick Revision
One-page CGPSC CSAT revision for logical reasoning — syllogism rules, alphabet codes, relation terms, direction rules and seating formulas in tables.
Every rule from Syllogisms, Coding-Decoding, Blood Relations, Direction Sense and Seating Arrangement on one page.
How to use this sheet
Scan top to bottom the week before Prelims. Bold lines are the rules examiners test most often; the warning boxes are the traps the wrong options are built on. If a rule surprises you, go back to the topic page and redo its speed drill.
Syllogisms
| Type | Form | Distributes |
|---|---|---|
| A | All S are P | Subject |
| E | No S is P | Both |
| I | Some S are P | Neither |
| O | Some S are not P | Predicate |
- “Some” = at least one, possibly all.
- Conversion: A → Some P are S; E → No P is S; I → Some P are S; O → no conversion.
| Pair (aligned X–Y, Y–Z) | Conclusion |
|---|---|
| A + A | All X are Z |
| A + E | No X is Z |
| E + A | Some Z are not X |
| E + I | Some Z are not X |
| I + A | Some X are Z |
| I + E | Some X are not Z |
| Anything else | No definite conclusion |
- Definite = true in every diagram. Possibility = true in at least one diagram (fails only if it contradicts).
- Either-or: same subject and predicate + neither follows alone + an I–O, A–O or E–I pair.
Favourite MCQ trap
“All S are P” does not give “All P are S”. And “Either I or II” is wrong whenever one of the two already follows on its own.
Coding-Decoding
| Fact | Detail |
|---|---|
| EJOTY | E = 5, J = 10, O = 15, T = 20, Y = 25 |
| Reverse partner | Positions add to 27 (A–Z, B–Y, C–X, D–W, E–V, F–U, G–T, H–S, I–R, J–Q, K–P, L–O, M–N) |
| Halves | A–M = 1–13; N–Z = 14–26 |
| Wrap-around | After Z comes A; before A comes Z |
| Rule-finding | Write word over code; check the shift of every letter; test for reversal first |
| Sentence codes | Shared words ↔ shared codes; two shared words with two shared codes → order cannot be determined |
| Substitution | Find the real answer, then give its code name |
Blood Relations
| Chain | Hindi | Chain | Hindi |
|---|---|---|---|
| Father’s brother | चाचा / ताऊ | Mother’s brother | मामा |
| Father’s sister | बुआ | Mother’s sister | मौसी |
| Brother’s son | भतीजा | Sister’s son | भांजा |
| Son’s son | पोता | Daughter’s son | नाती |
| Wife’s brother | साला | Sister’s husband | जीजा |
| Son’s wife | बहू | Daughter’s husband | दामाद |
- Method: draw the tree — double line = couple, vertical line = parent–child; mark gender only when given.
- Photograph chains: start from “my …” and move outward; collapse loops (“his son’s father” = himself).
- “Only” removes every other candidate.
- Direction of the answer: “How is P related to R?” = what P is to R.
Favourite MCQ trap
“E is the sister of D” fixes E as female — D’s gender stays unknown. “Cannot be determined” is often right — but only when the missing gender actually changes the answer.
Direction Sense
| Fact | Detail |
|---|---|
| Clockwise order | N 0°, NE 45°, E 90°, SE 135°, S 180°, SW 225°, W 270°, NW 315° |
| Right / left turn | 90° clockwise / anticlockwise from the current facing |
| Net displacement | \( x \) = east − west; \( y \) = north − south |
| Distance from start | \( \sqrt{x^2 + y^2} \) |
| Triples | 3-4-5, 6-8-10, 5-12-13, 8-15-17, 7-24-25, 20-21-29 |
| Shadows | Morning → shadow west; evening → shadow east |
Favourite MCQ trap
“Where is he from the start?” (position) is not “Which way is he facing?” (last leg). And distance from the start is never the sum of the legs.
Seating Arrangement
| Situation | Left | Right |
|---|---|---|
| Row facing north | Your left on paper | Your right |
| Row facing south | Your right on paper | Your left |
| Circle facing centre | Clockwise | Anticlockwise |
| Circle facing outward | Anticlockwise | Clockwise |
| Formula | Use |
|---|---|
| Total = L + R − 1 | Position from both ends known |
| From right = \( n - k + 1 \) | Convert one end to the other |
| Between = \( \lvert a - b \rvert - 1 \) | Both positions from the same end |
| Opposite = \( \frac{n}{2} \) seats away | Even circle of \( n \) |
- Clue order: definite → relative → negative; keep both cases until one is eliminated; re-check every clue at the end.
Don’t Confuse
| This | vs | That |
|---|---|---|
| All S are P → Some P are S | All S are P → All P are S (invalid) | |
| Reverse alphabet (A ↔ Z) | Reverse order (word written backwards) | |
| भतीजा (brother’s son) | भांजा (sister’s son) | |
| Distance travelled (sum of legs) | Distance from start (\( \sqrt{x^2 + y^2} \)) | |
| Facing centre: left = clockwise | Facing outward: left = anticlockwise |
Favourite MCQ trap
Most reasoning errors are reading errors: the wrong facing direction, the wrong reference person, or a gender that was never stated. Read the question once more before marking.
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