RRB NTPC · Bite-size lessons

Similarities and Differences

About 7 min · General Intelligence and Reasoning · English

Time worked out from the lesson's 513 words at 150 words a minute, plus a minute for each question.

Similarities and Differences is a reasoning topic in RRB NTPC that tests your ability to identify patterns, group items logically, and spot the outlier. These questions appear as "Odd One Out" or "Classification" problems where you're given 4-5 items and must find which doesn't belong, or which group shares a common property.

Key ideas

• Odd One Out principle: In a set of 4-5 items, exactly one does not share the defining property of the others. Your job is to identify the common property first, then find the exception.
• Classification by number properties: Numbers can be grouped by divisibility (multiples of 3, 5), type (prime, composite, perfect square, perfect cube), digit sum, or mathematical operations (sum of digits, product of digits).
• Letter-based patterns: Letters may be classified by position in alphabet (vowels vs consonants, first half vs second half), alphabetical order, positional values (A=1, B=2...), or letter clusters.
• Word classification: Words are grouped semantically (fruits, animals, metals, rivers) or by linguistic properties (starting letter, number of syllables, gender in nouns, verb vs noun).
• Mixed item classification: Questions may mix numbers with letters, or use real-world items (months, capitals, scientists, historical events) requiring general knowledge to identify categories.

Watch out for

• Rushing to the first pattern noticed → Missing the dominant pattern: You might see that three items are even numbers and jump to mark an odd number as the answer, but if four of the five are perfect squares and one isn't, the "perfect square" property is the intended grouping.
• Confusing necessary vs sufficient properties → Picking wrong odd one: Seeing "all are metals" and picking one because it's also magnetic doesn't work unless magnetism is the grouping rule. Stick to the property shared by the most items and cleanly distinguishing one.
• Overlooking semantic categories in words → Treating them as letter puzzles: Students sometimes analyze spellings or letter counts when the question is about meaning (fruits vs vegetables, rivers vs mountains). Read the words as concepts first; check letter patterns only if semantic grouping fails.

Quick reference

• Systematic check order: Numbers (prime/composite, perfect square/cube, divisibility) → Letters (vowel/consonant, position value, alphabetical order) → Words (semantic category, linguistic property) → Mixed (apply domain …
• Three out of four/five rule: The odd one is typically the single exception to a rule followed by 3 or 4 others.
• Prime check shortcut: Numbers under 10 primes are 2,3,5,7. For larger numbers, test divisibility by small primes up to the square root.
• Perfect squares/cubes: Memorize up to 15² and 10³ to instantly recognize or eliminate candidates.
• Letter position quick reference: A-M (1-13) first half, N-Z (14-26) second half; vowels A(1), E(5), I(9), O(15), U(21).

Check yourself: 3 questions

This lesson is cut from the topic's note, not rewritten. Fact-checked on 18 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.

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