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Classification

Reasoning · Verbal Reasoning

7 Part1 worked examples5 practice questions

Suppose your bag holds an apple, a mango, a banana, grapes and a potato. Mother says, “Put these in the fruit basket.” You at once take the potato out, because four things are fruits and the potato is a vegetable. That is classification — putting things into a group by a shared property, and spotting the odd one out that does not fit.

In the exam the same job is done with four or five options. The question never states the rule; you must find out in which property the other options are alike. The one to which that property does not apply is the answer.

The chapter teaches four kinds of question: (1) the odd word, (2) the odd pair of words, (3) the odd letter or group of letters, (4) the odd number or pair of numbers. Each kind starts from the very basics — places of letters, prime numbers, the lists of squares and cubes, all built by ourselves.

How to use this chapter

  1. Read — each part first explains the idea, then shows how to catch the property.
  2. Study the solved example — in the boxes marked “Example” the full solution is open, step by step.
  3. Try it yourself — in the “Try it yourself first” questions the solution is hidden. Think first, then choose; take the hint if stuck.
  4. Know the level — every question is marked Basic, Standard or Advanced. Make the basic ones solid first.
NoteThe questions you have solved are remembered in this browser. Look at the panel on the right (the “Contents” button on a phone) to see how many you have got right.
1

Foundation — how to catch the odd one

Find the property → test every option → pick the lonely one

The core idea of classification, four steps to find the property, what to do when more than one logic seems possible, and a map of the four kinds.

The idea of the odd one out

What the majority share — and who lacks it

A four-step method to identify the shared property and three rules for using it.

Every classification question hides a shared property. With four options three of them carry it, and with five options four of them do; only one does not. Finding that one is the question. Here are some common kinds of “property”:

Kind of propertyExampleOdd one
Members of one classmango, banana, apple, potato, grapespotato (a vegetable, not a fruit)
The same job or useknife, scissors, blade, penpen (writes, does not cut)
The same material or buildgold, silver, copper, brassbrass (an alloy; the rest are pure metals)
The same pattern of lettersBD, FH, JL, PQPQ (the rest skip one letter)
The same number property9, 16, 25, 27, 3627 (the rest are perfect squares)
Four steps to find the property
1. Read all the options carefully2. Think of a shared property from two or three of them3. Try that property on every option4. The one left alone is the answer; if more than one is left, change the property

Three rules that save you from confusion

  1. Exactly one option must be left out. If your property leaves two options out, it is not the examiner’s property. Drop it and look for a new one.
  2. Choose the most specific property. Often a big class fits all options (all five are animals). Then look for a narrower sub-property (four herbivores, one carnivore).
  3. “The best logic” — sometimes two properties single out different options. Take the stronger, more direct one that a school syllabus would use.
Make it a habitNever choose an answer just because “it feels different”. Before choosing, say one sentence: “All the others are …, and this one is not.” If you can complete that sentence, the answer is firm.
Example 1 · Basic
Pick the odd word out: the word that is not like the other words. (a) apple (b) pear (c) nurse (d) mango (e) orange
Solution, step by step
  1. 1Find what the others share: apple, pear, mango and orange — these are all fruits.
  2. 2Now test the remaining word nurse: it belongs to “professions”, not to “fruits”.
  3. 3So the odd one out is nurse.
Answer nurse
Here the shared property is a whole class (fruits); the odd word belongs to another class.
BasicTry it yourself first
Pick the odd word out: the word that is not like the other words.
BasicTry it yourself first
Pick the odd word out: the word that is not like the other words.

The four kinds of question — a map

What to check in each kind

How to recognise questions on words, word pairs, letters and numbers, and the first checks for each.

Recognise the kind of question as soon as you see it, because each kind has its own checks. The map below is the summary of the whole chapter:

What the options look likeKindFirst checksNext part
Rose, Lotus, Tulip, BanyanOdd wordclass? use? material? habitat? food?Words
Cat : Kitten, Cow : CalfOdd pair of wordsthe relation of each pair in a sentence; is the order reversed?Words
A, E, K, O, UOdd lettervowel / consonant, even / odd place, halvesLetters
CEG, FHJ, KMO, PQROdd group of letterswrite the places and see gaps and sumsLetters
17, 23, 29, 33, 41Odd numberprime? square? cube? multiple? digit sum?Numbers
4 : 16, 5 : 25, 6 : 30Odd pair of numbersratio, difference, square, cubeNumbers
TrickIn questions on letters and numbers look at the place or value, not the look. Rewrite each letter by its place (A = 1 … Z = 26); an odd letter often becomes an odd number.
BasicTry it yourself first
Pick the odd word out: the word that is not like the other words.
BasicTry it yourself first
Choose the letter that is different from the rest.
BasicTry it yourself first
Choose the number that is different from the rest.
2

Classification of words

The odd word and the odd pair of words

Spotting the outsider among words of one class, catching the property hidden inside one big class, and choosing the odd pair by its relation.

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The odd word — a member of another class

Four from one class, one from another

Recognising the class, the trap of neighbouring classes and the common confusions (bat, whale, spider …).

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The odd word — the hidden property

All from one class, yet one differs

When all five words are from one big class, finding the sub-property four share (habitat, food, material, state, border …).

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The odd pair of words

The same relation in four pairs, a different one in one

Putting the relation of a pair into a sentence, the list of relations, and the trap of reversed order or look-alike relations.

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3

Classification of letters

The odd letter, the odd group of letters, letter + number

Turning letters into their places (numbers) to find the odd letter or group.

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The odd letter

Five letters, one shared feature in four

Vowels and consonants, even and odd places, the two halves, multiples, prime places and letters of straight lines.

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The odd group of letters

Groups of 2, 3 or 4 letters: gaps, sums, vowels, shape

Turning the letters of each group into numbers and running four tests: equal gaps, a fixed sum, the number of vowels and the shape of consecutive letters.

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Groups with letters and numbers

Like DG3, KP5: two letters and a number

In groups of two letters and a number, replacing the letters by their places and finding the add/subtract rule with the number.

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4

Classification of numbers

The odd number, the odd digit pattern, the odd pair

Prime, square, cube, multiple, the make-up of the digits and the relations in pairs of numbers — all the tests that apply to numbers.

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The odd number — lists to recognise

Prime, square, cube, powers of 2, multiples

Lists of the kinds of numbers and the divisibility tests, so that every number can be identified at once.

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The odd number — the make-up of its digits

In 3–4 digit numbers: the sum, product and order of digits

When numbers are long, looking at their digits instead of the whole number: sum, product, even or odd, increasing order, palindromes, reversing.

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The odd pair or group of numbers

Ratio, difference, square, cube; sum and product

Finding the relation between the numbers of a pair (a : b) or a triple (a, b, c) and choosing the one that breaks it.

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5

Strategy guide

The order of checks for each kind and the slips to avoid

What to check first in each of the four kinds, the common traps and time-savers.

The order of checks

The first step on seeing the options

A table for choosing the tests according to the form of the options.

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Common traps and time-savers

Where marks are lost

The mistakes that keep happening in classification and how to avoid them.

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6

Mixed practice

All kinds mixed — first spot the kind, then solve

Questions on words, pairs, letters and numbers together, in three levels.

Basic practice

One property, one step

Plain classes, simple sub-properties, simple relations, vowels and even/odd, and direct number lists.

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Standard practice

Neighbouring classes, inner properties, tricky relations and digit patterns

Outsiders from neighbouring classes, properties in India and Rajasthan, reversed order, letter sums, multiples and pairs of numbers.

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Advanced practice

Subtle properties, five options, mixed rules

Choosing the right one of two or three possible properties, fine splits in Rajasthan and science, long numbers and triples.

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7

Revision — cards

Flip each card and test yourself

Think of the answer yourself first, then flip.

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