6.3 Classification (Similarities & Differences)

Why This Matters

Classification questions ask you to find the odd one out or group items by a shared property. They appear in 4 to 6 of the 30 Reasoning marks and are quick wins once your property-spotting discipline is sharp. The four flavors are word, number, letter, and mixed classification.

Word Classification (Odd-One-Out)

Given 4 to 5 words, find the one that does not share the common property.

Steps:

1. Identify the obvious category — animals, professions, vehicles, fruits.
2. Find a finer property — habitat, profession type, body part, plant part.
3. If no obvious property emerges, fall back to spelling: letter count, vowel count, doubled letters, palindromes.

Number Classification

Given 4 to 5 numbers, find the odd one by checking in this order:

Letter Classification

Given 4 to 5 letter pairs or groups, find the odd one by checking:

• Vowel count in the group.
• Position of letters in the alphabet (A = 1, B = 2, …, Z = 26).
• Whether the group is all consonants, all vowels, or mixed.
• Skipped-letter pattern (AC skips B; DF skips E).
• Reversal or palindrome (NITIN reads the same backwards).

For letter pairs, the most common RRB pattern is a fixed alphabetical gap. Compute gap = position of second letter minus position of first; three pairs share the gap and one does not.

Similarities and Analogies

The RRB variant of similarity asks "which of these goes with X?" or "find the like pair." Match by:

Differences

Difference questions reverse similarities: the answer is the option that does NOT fit the analogy. The technique is identical — identify the relation in the stem pair, then check each option pair for the same relation. The pair with a different relation is the odd one.

Worked example: "Knife : Cut :: ?" Choose the option that does NOT fit.

• Scissor : Cut — tool : function. Match.
• Axe : Chop — tool : function. Match.
• Hammer : Hit — tool : function. Match.
• Wood : Burn — material : action (not tool : function). Odd one. Answer: Wood : Burn.

Mixed Letter-Number Questions

Mixed items combine a letter and a number (e.g., A1, C3, F6). The usual trick is to convert the letter to its alphabetical position and check whether the position equals the number. If three items match and one does not, that one is the answer. Always use A = 1, B = 2, …, Z = 26 unless the question specifies otherwise.

Worked Example 1 (Number)

Find the odd one: 8, 27, 64, 100.

• 8 = 2³, 27 = 3³, 64 = 4³ — all perfect cubes.
• 100 = 10² — a perfect square, but not a cube. Answer: 100.

Worked Example 2 (Word)

Which does NOT belong: Tomato, Carrot, Radish, Potato?

• Carrot, Radish, Potato are root vegetables (grow underground).
• Tomato is botanically a fruit and grows above ground. Answer: Tomato.

Worked Example 3 (Letter Pair)

Find the odd letter pair: AC, DF, GI, JK.

• AC: A = 1, C = 3, gap 2.
• DF: D = 4, F = 6, gap 2.
• GI: G = 7, I = 9, gap 2.
• JK: J = 10, K = 11, gap 1. Answer: JK (consecutive letters, gap 1).

Worked Example 4 (Mixed)

Find the odd one: A1, C3, F6, J10, M14.

• A = 1 → 1. Match.
• C = 3 → 3. Match.
• F = 6 → 6. Match.
• J = 10 → 10. Match.
• M = 13 → should be 13, but labeled 14. Mismatch. Answer: M14.

Exam Traps

• Test prime status first; it is the most common RRB trap. 91 is not prime (7 × 13); 87 is not prime (3 × 29); 51 is not prime (3 × 17).
• "Vowel count" can be ambiguous in Indian English (Y is treated as a consonant unless stated). The exam usually avoids Y.
• For analogies, check the direction (Knife : Cut is "tool : function"; Cut : Knife reverses it). Direction matters — the answer must preserve the relation in the same direction.