Notes for SSC CGL examinations — discover the rule shared by the majority, then prove which word, number, symbol or figure alone violates it.
Classification groups items using a common attribute or relationship. Odd-one-out identifies the item that alone fails that majority rule.
A sound answer needs two statements:
Rule: first three are flowers; mango is a fruit.
Prefer an objective, standard property over a subjective description. “Three are prime” is stronger than “three look mathematically special.”
| Common basis | Example majority | Typical outsider | Precision check |
|---|---|---|---|
| Taxonomic class | rose, lily, lotus | mango | all three are flowers, not merely plants |
| Function/use | knife, scissors, razor | spoon | first three cut; spoon mainly scoops |
| Profession | doctor, nurse, surgeon | architect | first three are clinical health workers |
| Workplace | court, hospital, school | judge/doctor/teacher item may differ by relation | keep nouns at same relational level |
| Material | gold, silver, copper | coal | first three are metals |
| Living/non-living | oak, grass, fern | stone | biological class, not size |
| Part of speech | run, walk, jump | quick | verbs versus adjective |
| Degree | warm, hot, scorching | cold | three progress in same direction |
| Relation pair | author–book, painter–painting, composer–music | reader–book | creator–creation versus user–object |
| Young one/adult | calf–cow, foal–horse, cub–lion | goat–kid | direction reversal makes outsider |
“Tiger, lion, leopard” can share the narrow class big cats. “Cat” is also a feline but may be the outsider if the intended level is wild big cats.
Use the narrowest natural category that groups the majority uniquely.
Pen, pencil, paper and writer all relate to writing, but the first three are objects; writer is a person. “Associated with” is too broad.
When each option is a pair, classify the relationship, including direction.
“Bee–honey, cow–milk, hen–egg” are source/producer → product. “Silk–silkworm” reverses product → source and is odd.
| Property | Recognition | Examples |
|---|---|---|
| Parity | remainder on division by \(2\) | even: \(2k\); odd: \(2k+1\) |
| Prime/composite | number of positive factors | prime has exactly \(2\); \(1\) is neither |
| Perfect square | all prime-factor exponents even | \(1,4,9,16,25,\ldots\) |
| Perfect cube | all prime-factor exponents multiples of \(3\) | \(1,8,27,64,125,\ldots\) |
| Triangular number | \(T_n=n(n+1)/2\) | \(1,3,6,10,15,21,\ldots\) |
| Fibonacci-type | each term is sum of preceding two | \(1,1,2,3,5,8,\ldots\) |
| Divisibility | common factor/remainder pattern | multiples of \(3\), same remainder modulo \(m\) |
Numbers may share a divisor or the same remainder after division.
Example: \(11,17,23\) all leave remainder \(5\) on division by \(6\); \(29\) also does, so it is not odd under that rule. Always test all options.
\(1\) has only one positive factor, so it is neither prime nor composite. \(2\) is the only even prime.
Sets like \(2,3,5,9\) have \(9\) as composite outsider; sets like \(1,4,9,16\) may instead be all perfect squares—so context matters.
Check exact squares/cubes before accepting a visually close number.
A common outsider is \(63\) among \(25,49,63,81\): the others are odd squares.
Classify by digit sum, product, reversal, repetition, ascending/descending order, or relationship between digits.
Example: \(123,234,345\) have consecutive ascending digits; \(357\) does not. Verify the same step size, not just “digits rise.”
When each option contains a pair/triple, find the internal relation:
Example: \((3,9),(4,16),(5,25),(6,35)\): first three use \(b=a^2\); last violates.
With a small set, many properties may appear. Choose the simplest property shared by the largest group and uniquely violated by one.
Example \(8,27,64,100\): three are perfect cubes \(2^3,3^3,4^3\); \(100\) is not. Although \(100\) is the only three-digit number, “digit count” is a weaker incidental pattern than the clear power sequence.
| Feature | How to inspect | Examples |
|---|---|---|
| Alphabet position | convert with \(A=1,\ldots,Z=26\) | prime positions, multiples, equal gaps |
| Vowel/consonant | check \(A,E,I,O,U\) | three consonants, one vowel |
| Opposite letters | positions sum to \(27\) | AZ, BY, CX |
| Vertical symmetry | capital block form mirror test | A, H, I, M, O, T, U, V, W, X, Y |
| Horizontal symmetry | font-dependent block form | B, C, D, E, H, I, K, O, X in common block styles |
| Enclosed regions | count closed loops | A,D,O,P,Q,R often one; B often two |
| Straight/curved strokes | inspect construction | E,F,H versus C,O,S |
| Symbol function | arithmetic, comparison, punctuation | \(+,-,\times,\div\) versus \(=\) |
Visual letter properties depend on the printed form shown in the question. Judge the displayed glyph, not a memorised font list.
Check equal spacing, prime positions, square positions, or a common remainder.
This group advances by \(+4\). If one letter breaks the fixed gap, it is odd.
Draw the proposed mirror line mentally. A small tail or slant may destroy symmetry.
Do not combine vertical and horizontal symmetry as though they were the same property.
Possible bases include function, number of strokes, orientation, enclosure, or operator family.
First three can act as basic arithmetic operations in a binary expression; equals states a relation. But in another option set, \(=\) may join comparison signs. Context controls class.
| Feature | Questions |
|---|---|
| Boundary | open/closed? straight/curved? number of sides? |
| Internal elements | how many lines, dots, smaller shapes or intersections? |
| Position | inside/outside/on boundary? which corner/quadrant? |
| Shading | same fraction? alternate region? relative to marker? |
| Symmetry | vertical, horizontal, rotational? |
| Orientation | same figure rotated, reflected or genuinely changed? |
| Topology | number of enclosed regions, crossings or connected parts? |
If three figures are rotations of the same pattern and one is a mirror image, the mirror is odd. Track clockwise order of asymmetric elements.
Three options may have \(n\) sides and \(n\) internal dots, while one has the correct count but wrong dot location. Test combined invariants.
Different-looking figures can share the same number of closed loops. Count topological regions without being distracted by size or angle.
If one option differs in colour, another in size and another in direction, identify which feature forms a three-to-one split. Ignore a one-to-one visual quirk.
A candidate answer is not secure until you can say: “These three share property \(P\); this one does not.”
Search for a clean cluster of three before analysing each option independently. A visible three-to-one split is faster and less biased.
Ask: Are three items kinds of the same noun? If not, test same function, source, workplace or relation. Move from taxonomy to function, not vague association.
Run this fast sequence:
Stop when a simple property gives a unique three-to-one split.
Perfect squares can end only in \(0,1,4,5,6,9\); never \(2,3,7,8\). Cubes have fixed last-digit mappings.
Use the filter to reject, then confirm positives if needed.
Convert letters to positions only as far as needed. Sometimes three are even-position letters and one is odd-position.
For pairs, add alphabet positions. Three pairs may total \(27\); the outsider will not.
Boundary, Count, Position, Symmetry/shading. Check in the same order every time.
Use an asymmetric marker and rotate the whole pattern. If clockwise order stays, it belongs; if order reverses, it is a mirror outsider.
One item can look unusual in many ways. If you build the rule around it, you may miss the intended majority property.
“All are living things” may group every option. The intended class must produce a unique three-to-one split.
\(1\) is odd and a perfect square, but neither prime nor composite. Its classification depends on the tested property.
If three numbers are cubes and one is not, choosing the only three-digit item may use an accidental surface feature.
Symmetry and loops depend on how the capital is printed. Use the glyph shown, not a universal memorised claim.
Rotation preserves handedness; reflection reverses it. A notch or dot exposes the difference.
An option may share the correct side count but violate dot count, shading or position. Figural classification often uses two linked features.
Creator → creation differs from creation → creator. Paired options must share both relation and direction.
If your property excludes two items, it cannot determine one answer. Refine or replace it.
Define the club rule first; only then identify who cannot enter.
The intended property must yield exactly a \(3:1\) split in a four-option question.
Ask “kinds of what?” before accepting a loose shared topic. Natural class beats broad association.
Even/odd, Prime, Power, Divisibility/digits.
Opposite letters always total \(27\). Pair sums expose the outsider quickly.
Boundary, Count, Position, Symmetry/Shading—scan these four shelves in order.
Follow dots clockwise. Same cyclic order means rotation; reversed order signals reflection.
A valid rule should be natural, objective and isolate exactly one item without exceptions.