Reasoning practice

Classification Questions with Answers

Classification questions show four or five words, numbers or letter groups and ask you to pick the one that does not belong. You must find the common property of the group, then spot the item that breaks it. SSC CGL, CHSL and MTS, and RRB NTPC and Group D papers ask them often. The main tip is to test more than one property, such as type, use, parity or letter gap, before you decide.

Rules to remember

Find the property shared by most items. The odd one out is the item that does not have it.
Word groups: look for category (bird, fruit, metal), function, living or non-living, and where the item is found.
Number groups: test prime, square, cube, odd or even, multiples of a number, and digit sum.
Number pairs: find the operation linking the two numbers in each pair (for example, second = first x 2 + 1) and see which pair breaks it.
Letter groups: check the gaps between letters using alphabet positions, the count of vowels, and whether the group is reversed or in order.
Squares to remember: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225.
If two different properties each point to a different odd item, pick the property that fits all the other items most clearly.

Worked examples

Q1. Choose the odd one out: Sparrow, Eagle, Bat, Parrot

Sparrow, eagle and parrot are all birds. They lay eggs and have feathers.
A bat is a mammal. It gives birth to young ones and feeds them milk.
So bat is the item that does not belong to the group.

Answer: Bat

Q2. Choose the odd number out: 9, 16, 25, 36, 48

Check for perfect squares: 9 = 3 x 3, 16 = 4 x 4, 25 = 5 x 5, 36 = 6 x 6.
48 lies between 36 and 49, so it is not a perfect square.
Four numbers are squares and one is not, so 48 is the odd one.

Answer: 48

Q3. Choose the odd letter group: ACE, GIK, MOQ, SUW, BDG

Write alphabet positions: ACE = 1, 3, 5. GIK = 7, 9, 11. MOQ = 13, 15, 17. SUW = 19, 21, 23. BDG = 2, 4, 7.
In the first four groups the gaps are +2 and +2.
In BDG the gaps are +2 and +3, so it breaks the pattern.
Cross-check with vowels: each of the first four groups contains exactly one vowel, while BDG has none. This also points to BDG.

Answer: BDG

Shortcuts that save time

Check at least two properties, not just the first one that comes to mind. A quick second test often shows that the first guess was wrong, and a wrong guess costs negative marks.
For numbers, test squares, cubes and primes first. These three tests settle most classification sets in seconds.
If you are stuck between two options, look for the one that differs in the simplest way, such as a different type or a different parity. If still unsure, skip the question and return to it later.

Where this appears

SSC CGL Tier-1	General Intelligence & Reasoning section
SSC CHSL Tier-1	General Intelligence section
SSC MTS	Reasoning section
RRB NTPC CBT-1	General Intelligence & Reasoning section
RRB Group D CBT	General Intelligence & Reasoning section

Classification

Practice Set

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Three of the following four words belong to a group. Find the odd one out: Yellow, Green, Blue, Ganga

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