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Number & Letter Classification

General Intelligence & Reasoning · Classification (Odd One Out)

Useful for: SSC CGL, OSSC RHT — Regular High School Teacher, OSEPA Primary Teacher / JT Category-I, OSEPA Upper Primary — Arts, OSEPA Upper Primary — Science, OSSSC Govt Physical Education Teacher (PET), OSSSC Govt TGT Arts, OSSSC Govt TGT Science — CBZ

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OSSSC Govt TGT Science — PCM

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Overview

Number and letter odd-one-out items hide arithmetic or alphabet-position rules shared by all but one option.

Key points

Number checks: prime, even/odd, perfect square, cube, multiple of k, digit sum.
Pairs such as 3–9, 4–16, 5–25 test a square relation; 2–8, 3–27 test cubes.
Letter groups: consecutive letters, equal gaps, vowels, opposite letters.
Convert letters to positions and check differences.
If digits are involved, test digit sum and product.

Explanation

Three-letter groups like BCD, FGH, JKL share consecutive letters.
Number pairs like 12–144 and 13–169 follow n → n².
Look for a vowel or a repeated letter as the odd feature.
A rule must cover three options exactly.

Step by step

List properties.
Find the shared rule.
Pick the misfit.

Examples

2, 3, 5, 9, 11 → 9 (not prime).
BCD, FGH, JKL, MOP → MOP (others are consecutive letters).
12–144, 13–169, 14–196, 15–220 → 15–220 (15² = 225).

Traps and advanced points

Trap: Taking 1 as prime.
Trap: Checking only the first pair of a number-pair set.
Trap: Missing that a group contains a vowel.

Quick revision

Primes to 50.
Squares and cubes recognition.
Letter positions for gaps.

Practice MCQs

Find the odd one out: 7, 11, 13, 15
1. 11
2. 13
3. 15
4. 7
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Answer: (c) 15. 7, 11, 13 — prime numbers.
Find the odd one out: 16, 25, 36, 40
1. 36
2. 40
3. 16
4. 25
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Answer: (b) 40. 16=4^2, 25=5^2, 36=6^2 — perfect squares.
Find the odd one out: 8, 27, 64, 100
1. 100
2. 8
3. 27
4. 64
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Answer: (a) 100. 8=2^3, 27=3^3, 64=4^3 — perfect cubes.
Find the odd one out: 24, 36, 48, 50
1. 50
2. 24
3. 36
4. 48
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Answer: (a) 50. 24, 36, 48 — sab 12 se divisible (aur 4 se bhi).
Find the odd letter group: BD, FH, JL, MN
1. FH
2. JL
3. MN
4. BD
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Answer: (c) MN. BD, FH, JL me gap 2 (ek letter skip).
Find the odd one out: 3, 5, 7, 9
1. 5
2. 7
3. 9
4. 3
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Answer: (c) 9. 3, 5, 7 — prime numbers.
Find the odd letter group: CFI, GJM, KNQ, PSU
1. KNQ
2. PSU
3. CFI
4. GJM
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Answer: (b) PSU. CFI, GJM, KNQ me internal gap 3 (+3,+3).
Find the odd one out: 121, 144, 169, 200
1. 121
2. 144
3. 169
4. 200
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Answer: (d) 200. 121=11^2, 144=12^2, 169=13^2 — perfect squares.
Find the odd one out: 2, 3, 6, 7 (all prime?)
1. 2
2. 3
3. 7
4. 6
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Answer: (d) 6. 2, 3, 7 — prime numbers.
Find the odd letter group: AZ, BY, CX, DV
1. DV
2. AZ
3. BY
4. CX
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Answer: (a) DV. AZ, BY, CX — opposite-letter pairs (position sum 27: A+Z=27, B+Y=27, C+X=27).