Classification — SSC CGL Reasoning Notes

Concepts and rules

Classification gives 4 items: 3 share a property and 1 does not. SSC words it as 'select the odd word', 'select the odd pair' or 'select the one that does not belong to the group'.

The basis must be a property that exactly 3 items have. A property held by only 2 items splits the group 2–2 and cannot decide the answer.

The basis is something the 3 have in common, not something they all lack. 'The only metal' is a weak basis when 3 items share a clear category such as 'planet'.

Common bases: category (metal, fruit, instrument), place (state capital, river origin), use (unit vs instrument), habitat, type of sport, and the kind of thing produced.

Odd pair questions: each option is a pair; find the relation inside each pair (state–capital, worker–tool, animal–young). The odd pair has a different relation, or the same relation in reverse order.

Prefer the most specific shared property. 'All are nouns' or 'all are things' fits all 4 items and separates nothing.

A word can belong to 2 categories (Mercury is a planet and also a metal in English). Choose the meaning under which exactly 3 items form a group.

Method and shortcuts

Step 1: Write 2 or 3 labels for each item: what it is, where it is found, what it is used for.

Step 2: Look for a label that exactly 3 items carry; the remaining item is the answer.

Step 3: If 2 different items look odd, go one level deeper (string vs percussion, Himalayan vs peninsular) until one property splits the group 3–1.

Shortcut for odd pairs: say every pair in one fixed sentence ('B is the capital of A'); the pair that breaks the sentence is the answer.

Shortcut: ignore surface features such as word length or first letter unless the question is about letters; examiners plant them as traps.

When it fails: if all 4 items seem different, check the spelling pattern or letter positions; that kind of grouping is covered in Symbol and number grouping.

Example 1: Category

Question: Copper, Iron, Zinc, Glass. Which is the odd one?

Solution: Copper, iron and zinc are metals; glass is not a metal. The property 'metal' is shared by exactly 3 items.

Answer: Glass

Example 2: Choosing the right meaning

Question: Mercury, Venus, Mars, Moon. Which is the odd one?

Solution: Mercury, Venus and Mars are planets; the Moon is a natural satellite of the Earth. Mercury is also the name of a metal, but that property belongs to only 1 item, so it is not the basis.

Answer: Moon

Example 3: Odd pair

Question: Kolkata – West Bengal, Chennai – Tamil Nadu, Mumbai – Maharashtra, Kanpur – Uttar Pradesh. Which pair is odd?

Solution: Sentence: 'the first city is the capital of the state'. It holds for Kolkata, Chennai and Mumbai. Kanpur is a city of Uttar Pradesh but the capital is Lucknow.

Answer: Kanpur – Uttar Pradesh

Example 4: Going one level deeper

Question: Select the odd one. (a) Tabla (b) Mridangam (c) Sitar (d) Dholak

Solution: All 4 are Indian musical instruments, so 'instrument' does not separate them. Tabla, mridangam and dholak are drums (percussion); the sitar is a string instrument.

Answer: (c) Sitar

Example 5: Odd pair by relation

Question: Select the odd pair. (a) Tailor : Needle (b) Farmer : Field (c) Carpenter : Saw (d) Painter : Brush

Solution: Sentence: 'the worker uses B as a tool'. A needle, a saw and a brush are tools. A field is the farmer's workplace, so (b) has a different relation; a matching pair would be Farmer : Plough.

Answer: (b) Farmer : Field

Example 6: Rejecting a 2–2 split

Question: Select the odd one. (a) Godavari (b) Ganga (c) Yamuna (d) Kosi

Solution: 'Falls directly into the Bay of Bengal' is true for the Ganga and the Godavari, while the Yamuna and the Kosi join the Ganga. That is a 2–2 split, so it is not the basis.

Go deeper: the Ganga, the Yamuna and the Kosi rise in the Himalayas; the Godavari rises in the Western Ghats near Nashik and is a peninsular river. This splits the group 3–1.

Answer: (a) Godavari

Common mistakes

Choosing an item for a property only it has (Mercury as the only metal) when 3 items share a clear category (planets). Find the shared property first.

Accepting a 2–2 split as the answer. If your property gives 2 odd items, it is the wrong property.

Comparing words across pairs instead of the relation inside each pair. In odd-pair questions only the internal relation matters.

Missing a reversed pair: in Cow : Calf, Dog : Puppy, Kitten : Cat, Hen : Chick the relation is the same, but Kitten : Cat is in reverse order, so it is the odd pair.

Falling for a surface trap: word length or starting letter is a basis only when the question is about letters.

Practice questions

Q1. Select the odd one. (a) Hockey (b) Football (c) Chess (d) Cricket

Q2. Select the odd pair. (a) Cow : Calf (b) Dog : Puppy (c) Cat : Kitten (d) Lion : Den

Q3. Select the odd one. (a) Kilogram (b) Thermometer (c) Metre (d) Litre

Answers

Q1. (c) Hockey, football and cricket are outdoor team games played on a field; chess is an indoor board game for 2 players.

Q2. (d) The other pairs are animal : its young; a den is the lion's home.

Q3. (b) Kilogram, metre and litre are units of measurement; a thermometer is an instrument.

Quick revision

The basis is a property exactly 3 items share; the remaining item is the answer.

A 2–2 split means you have the wrong property; go one level deeper.

Odd pair: say each pair in one sentence and watch for reversed order.

For a word with 2 meanings, use the meaning that makes a group of 3.

Concepts and rules

In figure classification, 3 figures follow one rule and the remaining one breaks it. In these notes each figure is described in words: shapes, cells of a 3×3 grid (R1C1 is top-left, R3C3 bottom-right), directions and counts.

Counting bases: number of sides (odd or even), number of dots or lines, number of shaded cells. Count before you look at anything else.

Lines of symmetry: square 4, equilateral triangle 3, rectangle that is not a square 2, rhombus that is not a square 2, isosceles (non-equilateral) triangle 1, parallelogram with no right angle and unequal adjacent sides 0, regular polygon with n sides n.

Capital letters as figures: vertical mirror line in A, H, I, M, O, T, U, V, W, X, Y; horizontal mirror line in B, C, D, E, H, I, K, O, X; no mirror line in F, G, J, L, N, P, Q, R, S, Z (N, S and Z look the same after a 180° turn).

Rotation family: often 3 figures are the same shape turned through 90°, 180° or 270°, and the remaining one is its mirror image. A mirror image of a shape with no line of symmetry can never be produced by rotating it.

Grid rule for rotation by 90° clockwise: cell (r, c) goes to (c, 4 − r); for 180°: (4 − r, 4 − c). A left–right mirror sends (r, c) to (r, 4 − c).

Relative position: when each figure has 2 elements, the rule is often the angle and the turning direction from one element to the other (for example, the dot is always 135° clockwise from the arrow). Directions clockwise: N, NE, E, SE, S, SW, W, NW, each 45° apart.

Method and shortcuts

Step 1: Count sides, elements and shaded cells of every figure and look for a 3–1 split.

Step 2: If counts agree, check symmetry: how many mirror lines, and whether they are vertical or horizontal.

Step 3: If the figures are the same shape in different positions, rotate one of them by 90°, 180° and 270°; the figure that none of these turns produces is the odd one.

Step 4: For 2-element figures, measure the step count from the first element to the second going clockwise; the odd figure has a different count.

Shortcut: in an L-shaped figure, walk along the long arm towards the foot; if the foot turns right in 3 figures and left in 1, that 1 is the mirror image.

When it fails: if 2 figures look odd for 2 different reasons, keep looking for a property that splits the 4 figures exactly 3–1.

Example 1: Parity of sides

Question: Triangle, Pentagon, Hexagon, Heptagon. Which figure is odd?

Solution: Sides are 3, 5, 6 and 7. Three figures have an odd number of sides; the hexagon has an even number.

Answer: Hexagon

Example 2: Letter symmetry

Question: Treat the letters A, M, U, N as figures. Which is odd?

Solution: A, M and U each have a vertical mirror line. N has no mirror line at all; it only looks the same after a 180° turn.

Answer: N

Example 3: Shaded cells

Question: 4 grids of size 3×3 have 4, 6, 5 and 8 shaded cells. Which grid is odd?

Solution: 4, 6 and 8 are even; 5 is odd. The basis is the parity of the shaded count.

Answer: The grid with 5 shaded cells

Example 4: Lines of symmetry

Question: Select the odd figure. (a) square (b) rhombus that is not a square (c) rectangle that is not a square (d) parallelogram with no right angle and unequal adjacent sides

Solution: All 4 are quadrilaterals, so sides do not decide, and 'all sides equal' (square, rhombus) or 'all angles 90°' (square, rectangle) split them 2–2. Mirror lines: square 4, rhombus 2 (its diagonals), rectangle 2 (lines joining midpoints of opposite sides), the parallelogram 0.

So 3 figures have at least 1 mirror line and the parallelogram has none: folding it along any line never makes the halves coincide.

Answer: (d) the parallelogram

Example 5: Rotation family and mirror image

Question: Each figure shades 4 cells of a 3×3 grid. (a) R1C1, R2C1, R3C1, R3C2 (b) R1C3, R2C3, R3C3, R3C2 (c) R1C1, R1C2, R1C3, R2C1 (d) R1C2, R1C3, R2C3, R3C3. Which is odd?

Solution: (a) is an L: a column of 3 cells with a foot to the right at the bottom. Rotating (a) by 90° clockwise with (r, c) → (c, 4 − r) gives R1C3, R1C2, R1C1, R2C1, which is (c). Rotating (a) by 180° gives R3C3, R2C3, R1C3, R1C2, which is (d).

(b) is (a) reflected in a vertical line, (r, c) → (r, 4 − c): its foot points left. No rotation of an L produces this reversed L, so (b) is the odd one.

Answer: (b)

Example 6: Relative position with direction

Question: Each figure is a circle with an arrow and a dot on its rim. (a) arrow W, dot SE (b) arrow N, dot SE (c) arrow E, dot SW (d) arrow SW, dot N. Which is odd?

Solution: Count clockwise steps from the arrow to the dot in the order N, NE, E, SE, S, SW, W, NW. (b) N to SE is 3 steps; (c) E to SW is 3 steps; (d) SW to N is 3 steps (W, NW, N).

(a) W to SE clockwise is 5 steps (NW, N, NE, E, SE); it is 135° anticlockwise, not clockwise. Every figure shows a 135° angle, so only the turning direction separates (a).

Answer: (a)

Common mistakes

Calling a rotated figure a mirror image: always try all 3 rotations (90°, 180°, 270°) before calling a figure odd.

Ignoring direction when measuring angles: 135° clockwise and 135° anticlockwise are different rules.

Wrong symmetry facts: a general parallelogram has no line of symmetry, and N, S and Z have none either; they only have 180° rotational symmetry.

Stopping at the first difference: a figure may look different in size or position but still follow the rule; test the actual rule on all 4 figures.

Practice questions

Q1. Select the odd figure. (a) square (b) hexagon (c) octagon (d) pentagon

Q2. Treat these letters as figures and select the odd one. (a) S (b) H (c) X (d) O

Q3. Each figure shades 4 cells of a 3×3 grid. (a) R1C2, R1C3, R2C1, R2C2 (b) R1C2, R2C2, R2C3, R3C3 (c) R1C1, R1C2, R2C2, R2C3 (d) R2C2, R2C3, R3C1, R3C2. Select the odd one.

Answers

Q1. (d) Sides are 4, 6, 8 and 5; the pentagon is the only one with an odd number of sides.

Q2. (a) H, X and O have both a vertical and a horizontal mirror line; S has no mirror line.

Q3. (c) (a) is an S-shape; (b) is (a) turned 90° clockwise and (d) is (a) turned 180°. (c) is the mirror image (a Z-shape), which no rotation of (a) produces.

Quick revision

Order of checks: counts, symmetry, rotation family, relative position.

90° clockwise in a grid: (r, c) → (c, 4 − r); mirror: (r, c) → (r, 4 − c).

Mirror image of an asymmetric shape is never a rotation of it.

For 2 elements, measure the angle and the direction of turning.

Concepts and rules

Meaning-based classification groups words by sense. 3 words (or pairs) share a meaning relation and 1 does not. The words themselves are usually from one field, such as emotions or size.

Single words: 3 synonyms and 1 opposite (Happy, Glad, Joyful, Gloomy), or 3 words of the same strength and 1 much milder or stronger (Elated, Euphoric, Ecstatic, Content).

Word pairs: 3 synonym pairs and 1 antonym pair, or the reverse; check each pair on its own before comparing.

Degree pairs: 3 pairs go from weaker to stronger (Warm – Hot, Like – Love, Drizzle – Downpour) and 1 goes from stronger to weaker (Shout – Whisper). The direction is the basis.

Use the standard dictionary sense. Content means satisfied and calm; ecstatic, euphoric and elated mean intensely happy. A shade of meaning is a valid basis only when it is clear-cut.

All 4 words are normally the same part of speech; the oddity lies in meaning, not in grammar or spelling.

Method and shortcuts

Step 1: Give each word a 1-word meaning and a sign: + for the positive side, − for the negative side, and a strength mark (mild or strong).

Step 2: For single words, look for 3 with the same sign and strength; for pairs, label each pair S (synonym), A (antonym), U (rising degree) or D (falling degree).

Step 3: The label that appears 3 times is the group; the remaining word or pair is the answer.

Shortcut: in pair questions, an antonym pair is usually easiest to spot, so test 'opposite?' on each pair first.

Shortcut: for degree, read each pair as 'the second is a stronger form of the first'; the pair where this sentence is false is the answer.

When it fails: if 2 words seem odd, one of them probably differs only slightly; choose the word whose meaning is clearly different in sign or strength.

Example 1: 3 synonyms and 1 opposite

Question: Happy, Glad, Joyful, Gloomy. Which word is odd?

Solution: Happy, glad and joyful all mean pleased (+). Gloomy means sad and dark in mood (−).

Answer: Gloomy

Example 2: Odd pair by relation

Question: Begin – Start, Huge – Enormous, Brave – Bold, Rich – Poor. Which pair is odd?

Solution: Labels: S, S, S, A. The first 3 are synonym pairs; Rich – Poor is an antonym pair.

Answer: Rich – Poor

Example 3: Direction of degree

Question: Warm – Hot, Drizzle – Downpour, Like – Love, Shout – Whisper. Which pair is odd?

Solution: In the first 3 pairs the second word is a stronger form (labels U, U, U). A whisper is a much softer sound than a shout, so Shout – Whisper falls in degree (D).

Answer: Shout – Whisper

Example 4: Synonym group

Question: Select the odd word. (a) Brief (b) Concise (c) Succinct (d) Verbose

Solution: Brief, concise and succinct all mean expressed in few words. Verbose means using more words than needed, the opposite.

Answer: (d) Verbose

Example 5: Shade of meaning

Question: Select the odd word. (a) Elated (b) Euphoric (c) Content (d) Ecstatic

Solution: All 4 words are on the happy (+) side, so the sign does not decide. Elated, euphoric and ecstatic mean intensely happy, carried away with joy (strong). Content means quietly satisfied (mild).

The basis is strength: 3 strong, 1 mild.

Answer: (c) Content

Example 6: Harder vocabulary pairs

Question: Select the odd pair. (a) Candid – Frank (b) Prudent – Rash (c) Obstinate – Stubborn (d) Lucid – Clear

Solution: Candid and frank both mean open and honest; obstinate and stubborn both mean refusing to change one's mind; lucid means clear and easy to understand. These are 3 synonym pairs.

Prudent means careful and wise in judgement, while rash means acting without thinking, so (b) is an antonym pair.

Answer: (b) Prudent – Rash

Common mistakes

Judging by one familiar word: in (a) Candid – Frank, Frank looks like a name, but here it is an adjective meaning honest. Read each word in its usual adjective sense.

Mixing sign and strength: in Elated, Euphoric, Content, Ecstatic all are positive; looking only for an opposite finds nothing. Check strength next.

Ignoring direction in degree pairs: Shout – Whisper and Whisper – Shout are different; the order inside the pair matters.

Picking a rare word as odd only because it is unfamiliar: Succinct is unusual but means the same as brief.

Practice questions

Q1. Select the odd word. (a) Calm (b) Anger (c) Rage (d) Fury

Q2. Select the odd pair. (a) Ancient – Modern (b) Victory – Defeat (c) Famous – Renowned (d) Expand – Contract

Q3. Select the odd pair. (a) Smile – Laugh (b) Walk – Run (c) Hill – Mountain (d) Flood – Trickle

Answers

Q1. (a) Anger, rage and fury are all forms of anger; calm is the absence of it.

Q2. (c) The other 3 pairs are antonyms; famous and renowned are synonyms.

Q3. (d) In the first 3 pairs the second word is the bigger or stronger form; a trickle is far smaller than a flood, so the degree falls.

Quick revision

Label words with sign (+ or −) and strength (mild or strong).

Label pairs S, A, U or D; the label seen 3 times is the group.

Order inside a pair matters for degree.

Use the standard dictionary sense, not a guess from spelling.

Concepts and rules

Number classification: 3 numbers (or pairs, or triads) share a numerical property and 1 does not. The property should be something the 3 have, such as being prime or a perfect cube.

Single-number properties: prime, perfect square, perfect cube, even or odd, divisible by 3 (digit sum divisible by 3), by 5, by 11 (difference of alternate digit sums divisible by 11), and the digit sum itself.

Fake primes that SSC loves: 51 = 3 × 17, 57 = 3 × 19, 87 = 3 × 29, 91 = 7 × 13, 119 = 7 × 17, 133 = 7 × 19, 143 = 11 × 13. Test small divisors before calling a number prime.

Pairs (a : b) and triads (a, b, c): find the relation inside each set, such as b = a³ or a = b × c, and look for the set that breaks it.

Letter clusters: write positions (A=1 … Z=26) and compute the gaps between neighbouring letters. ACE has gaps +2, +2; RTW has gaps +2, +3.

Other letter bases: opposite pairs (positions add to 27), number of vowels, letters in alphabetical order, and position sums.

Method and shortcuts

Step 1: Test the fastest properties on all 4 items: parity, prime, square, cube.

Step 2: If nothing splits 3–1, go to digits: digit sum, digit product, difference of digits, reversal.

Step 3: For pairs and triads, find the rule on 2 sets that obviously agree, then test the other 2.

Step 4: For letters, write the gaps of every cluster as a short signature (+2, +2) and pick the cluster with a different signature.

Shortcut: a perfect square ends in 0, 1, 4, 5, 6 or 9, so a number ending in 2, 3, 7 or 8 is never a square.

When it fails: if your property makes 2 items odd, it is the wrong property; try the next one on the list.

Example 1: Fake prime

Question: 17, 23, 29, 33. Which number is odd?

Solution: 17, 23 and 29 are prime. 33 = 3 × 11 is composite.

Answer: 33

Example 2: Perfect cubes

Question: 125, 216, 343, 300. Which number is odd?

Solution: 125 = 5³, 216 = 6³, 343 = 7³. 300 lies between 6³ = 216 and 7³ = 343, so it is not a cube.

Answer: 300

Example 3: Letter gaps

Question: ACE, GIK, MOQ, RTW. Which cluster is odd?

Solution: A(1) C(3) E(5): +2, +2. G(7) I(9) K(11): +2, +2. M(13) O(15) Q(17): +2, +2. R(18) T(20) W(23): +2, +3.

Answer: RTW

Example 4: Number pairs

Question: Select the odd pair. (a) 3 : 27 (b) 4 : 64 (c) 5 : 120 (d) 6 : 216

Solution: 3³ = 27, 4³ = 64 and 6³ = 216, so the rule is b = a³. 5³ = 125, not 120.

Answer: (c) 5 : 120

Example 5: Triads

Question: Select the odd set. (a) (56, 8, 6) (b) (36, 9, 4) (c) (42, 6, 7) (d) (63, 9, 7)

Solution: Check first = second × third: (b) 9 × 4 = 36, (c) 6 × 7 = 42, (d) 9 × 7 = 63. In (a), 8 × 6 = 48, not 56 (56 would need 8 × 7).

Answer: (a) (56, 8, 6)

Example 6: Opposite-letter clusters

Question: Select the odd cluster. (a) AZBY (b) GTHR (c) CXDW (d) EVFU

Solution: Split each cluster into 2 pairs and add positions. AZ: 1 + 26 = 27, BY: 2 + 25 = 27. CX: 3 + 24 = 27, DW: 4 + 23 = 27. EV: 5 + 22 = 27, FU: 6 + 21 = 27.

GT: 7 + 20 = 27 but HR: 8 + 18 = 26. The opposite of H is S, so GTHS would fit; GTHR breaks the rule.

Answer: (b) GTHR

Common mistakes

Calling 91, 87 or 51 prime: test division by 3 and 7 every time.

Forgetting that 64 is both 8² and 4³, and 729 is both 27² and 9³: such numbers can belong to 2 groups, so decide by the property that splits 3–1.

Checking only the first gap of a letter cluster: RTW starts like the others (+2) and differs only at the second gap.

Testing a triad in the wrong order: (56, 8, 7) fits 'first = second × third', but (8, 56, 7) does not; keep the order given.

Practice questions

Q1. Select the odd number. (a) 361 (b) 290 (c) 169 (d) 289

Q2. Select the odd cluster. (a) BDF (b) HJL (c) MOQ (d) RSU

Q3. Select the odd number. (a) 235 (b) 451 (c) 529 (d) 613

Answers

Q1. (b) 361 = 19², 169 = 13², 289 = 17²; 290 is not a perfect square.

Q2. (d) BDF, HJL and MOQ have gaps +2, +2; R(18) S(19) U(21) has gaps +1, +2.

Q3. (c) Digit sums: 2 + 3 + 5 = 10, 4 + 5 + 1 = 10, 6 + 1 + 3 = 10, but 5 + 2 + 9 = 16.

Quick revision

Order of tests: parity, prime, square, cube, then digits.

Fake primes: 51, 57, 87, 91, 119, 133, 143.

Letters: write positions, compare gap signatures, check sums of 27.

A property that makes 2 items odd is the wrong property.