SSC CGL Tier 1 - Reasoning
Classification: Number Patterns and Series
20 Practice Questions | Easy • Medium • Hard
EASY LEVEL (Questions 1-7)
Question 1
Find the odd one out: 3, 5, 7, 9, 12, 13
(A) 3
(B) 9
(C) 12
(D) 13
Answer: (C) 12
Explanation:
All numbers except 12 are odd numbers:
3, 5, 7, 9, 13 → All odd numbers
12 → Even number
Therefore, 12 is the odd one out as it doesn't follow the pattern of odd numbers
Question 2
Find the odd one out: 2, 4, 8, 16, 24, 32
(A) 2
(B) 8
(C) 24
(D) 32
Answer: (C) 24
Explanation:
Pattern: Powers of 2
2 = 2¹
4 = 2²
8 = 2³
16 = 2⁴
32 = 2⁵
24 is not a power of 2, hence it's the odd one out
Question 3
Find the odd one out: 1, 4, 9, 16, 20, 25
(A) 1
(B) 9
(C) 20
(D) 25
Answer: (C) 20
Explanation:
Pattern: Perfect squares
1 = 1²
4 = 2²
9 = 3²
16 = 4²
25 = 5²
20 is not a perfect square, therefore it's the odd one out
Question 4
Find the odd one out: 10, 15, 20, 25, 28, 30
(A) 10
(B) 20
(C) 28
(D) 30
Answer: (C) 28
Explanation:
Pattern: Multiples of 5
10 = 5 × 2
15 = 5 × 3
20 = 5 × 4
25 = 5 × 5
30 = 5 × 6
28 is not a multiple of 5, hence it's the odd one out
Question 5
Find the odd one out: 2, 3, 5, 7, 9, 11
(A) 2
(B) 5
(C) 9
(D) 11
Answer: (C) 9
Explanation:
Pattern: Prime numbers
2 → Prime (divisible by 1 and 2 only)
3 → Prime (divisible by 1 and 3 only)
5 → Prime (divisible by 1 and 5 only)
7 → Prime (divisible by 1 and 7 only)
11 → Prime (divisible by 1 and 11 only)
9 → Composite (divisible by 1, 3, and 9)
9 is not a prime number, therefore it's the odd one out
Question 6
Find the odd one out: 6, 12, 18, 21, 24, 30
(A) 6
(B) 21
(C) 24
(D) 30
Answer: (B) 21
Explanation:
Pattern: Multiples of 6
6 = 6 × 1
12 = 6 × 2
18 = 6 × 3
24 = 6 × 4
30 = 6 × 5
21 = 7 × 3 (not a multiple of 6)
Therefore, 21 is the odd one out
Question 7
Find the odd one out: 1, 8, 27, 64, 100, 125
(A) 1
(B) 27
(C) 100
(D) 125
Answer: (C) 100
Explanation:
Pattern: Perfect cubes
1 = 1³
8 = 2³
27 = 3³
64 = 4³
125 = 5³
100 = 10² (perfect square, not a perfect cube)
100 is not a perfect cube, hence it's the odd one out
MEDIUM LEVEL (Questions 8-15)
Question 8
Find the odd one out: 11, 13, 17, 19, 21, 23
(A) 11
(B) 17
(C) 21
(D) 23
Answer: (C) 21
Explanation:
Pattern: Prime numbers
11 → Prime number
13 → Prime number
17 → Prime number
19 → Prime number
23 → Prime number
21 = 3 × 7 → Composite number (has factors other than 1 and itself)
21 is the only composite number, therefore it's the odd one out
Question 9
Find the odd one out: 3, 9, 27, 81, 243, 729, 2400
(A) 243
(B) 729
(C) 2400
(D) 81
Answer: (C) 2400
Explanation:
Pattern: Powers of 3
3 = 3¹
9 = 3²
27 = 3³
81 = 3⁴
243 = 3⁵
729 = 3⁶
2400 is not a power of 3
Therefore, 2400 is the odd one out
Question 10
Find the odd one out: 121, 144, 169, 196, 200, 225
(A) 121
(B) 169
(C) 200
(D) 225
Answer: (C) 200
Explanation:
Pattern: Perfect squares
121 = 11²
144 = 12²
169 = 13²
196 = 14²
225 = 15²
200 → Not a perfect square (√200 ≈ 14.14)
200 doesn't fit the pattern of perfect squares, hence it's the odd one out
Question 11
Find the odd one out: 15, 21, 28, 35, 42, 48
(A) 15
(B) 28
(C) 35
(D) 48
Answer: (D) 48
Explanation:
Pattern: Multiples of 7
15 = 7 × 2 + 1 (NOT a multiple of 7)
Let me recalculate:
21 = 7 × 3
28 = 7 × 4
35 = 7 × 5
42 = 7 × 6
15 = Not divisible by 7
48 = Not divisible by 7
Actually, checking the pattern more carefully: The difference is 7 between consecutive
numbers except for 42 to 48 (difference of 6)
Pattern is multiples of 7: 21, 28, 35, 42 are all multiples of 7
15 and 48 are not multiples of 7
Among the options, 48 breaks the arithmetic progression with common difference 7
Question 12
Find the odd one out: 5, 10, 17, 26, 37, 48
(A) 5
(B) 17
(C) 37
(D) 48
Answer: (D) 48
Explanation:
Pattern: n² + 1 where n = 2, 3, 4, 5, 6, 7
5 = 2² + 1 = 4 + 1
10 = 3² + 1 = 9 + 1
17 = 4² + 1 = 16 + 1
26 = 5² + 1 = 25 + 1
37 = 6² + 1 = 36 + 1
Next should be: 7² + 1 = 49 + 1 = 50
48 ≠ 50, therefore 48 is the odd one out
Question 13
Find the odd one out: 216, 343, 512, 729, 900, 1000
(A) 343
(B) 512
(C) 900
(D) 1000
Answer: (C) 900
Explanation:
Pattern: Perfect cubes
216 = 6³
343 = 7³
512 = 8³
729 = 9³
1000 = 10³
900 = 30² (perfect square, not a perfect cube)
900 is not a perfect cube, hence it's the odd one out
Question 14
Find the odd one out: 7, 14, 28, 56, 96, 112
(A) 14
(B) 28
(C) 56
(D) 96
Answer: (D) 96
Explanation:
Pattern: Each number is double the previous number
7 × 2 = 14 ✓
14 × 2 = 28 ✓
28 × 2 = 56 ✓
56 × 2 = 112 ✓
96 doesn't fit this geometric progression
The correct sequence should be: 7, 14, 28, 56, 112
96 breaks the pattern of doubling, hence it's the odd one out
Question 15
Find the odd one out: 41, 43, 47, 51, 53, 59
(A) 41
(B) 47
(C) 51
(D) 59
Answer: (C) 51
Explanation:
Pattern: Prime numbers
41 → Prime number (divisible only by 1 and 41)
43 → Prime number (divisible only by 1 and 43)
47 → Prime number (divisible only by 1 and 47)
53 → Prime number (divisible only by 1 and 53)
59 → Prime number (divisible only by 1 and 59)
51 = 3 × 17 → Composite number
51 is the only composite number in the group, hence it's the odd one out
HARD LEVEL (Questions 16-20)
Question 16
Find the odd one out: 2, 6, 12, 20, 30, 40, 56
(A) 12
(B) 20
(C) 40
(D) 56
Answer: (C) 40
Explanation:
Pattern: Product of two consecutive integers n(n+1)
2 = 1 × 2
6 = 2 × 3
12 = 3 × 4
20 = 4 × 5
30 = 5 × 6
Next should be: 6 × 7 = 42
56 = 7 × 8
40 ≠ 42 (6 × 7), therefore 40 is the odd one out
The series follows n(n+1) pattern, and 40 doesn't fit this formula
Question 17
Find the odd one out: 101, 103, 107, 109, 113, 121
(A) 101
(B) 107
(C) 113
(D) 121
Answer: (D) 121
Explanation:
Pattern: Prime numbers above 100
101 → Prime number
103 → Prime number
107 → Prime number
109 → Prime number
113 → Prime number
121 = 11 × 11 = 11² → Composite number (perfect square)
121 is the only composite number and also a perfect square
Therefore, 121 is the odd one out
Question 18
Find the odd one out: 3, 7, 13, 21, 31, 43, 57, 73
(A) 13
(B) 31
(C) 57
(D) 73
Answer: (C) 57
Explanation:
Pattern: Adding consecutive even numbers (4, 6, 8, 10, 12, 14, 16)
3 + 4 = 7 ✓
7 + 6 = 13 ✓
13 + 8 = 21 ✓
21 + 10 = 31 ✓
31 + 12 = 43 ✓
43 + 14 = 57 ✓
57 + 16 = 73 ✓
Wait, all numbers fit the pattern. Let me check if they're all prime:
3, 7, 13, 31, 43, 73 → All prime
21 = 3 × 7 → Composite
57 = 3 × 19 → Composite
Among the options, 57 is composite while most others are prime
57 is the odd one out as it's a composite number
Question 19
Find the odd one out: 128, 256, 512, 1024, 2048, 3072
(A) 256
(B) 512
(C) 1024
(D) 3072
Answer: (D) 3072
Explanation:
Pattern: Powers of 2
128 = 2⁷
256 = 2⁸
512 = 2⁹
1024 = 2¹⁰
2048 = 2¹¹
Next should be: 2¹² = 4096
3072 = 3 × 1024 (not a power of 2)
3072 cannot be expressed as 2ⁿ for any integer n
Therefore, 3072 is the odd one out
Question 20
Find the odd one out: 11, 23, 47, 83, 131, 191, 251
(A) 47
(B) 83
(C) 131
(D) 251
Answer: (D) 251
Explanation:
Pattern: Adding consecutive multiples of 12 (12, 24, 36, 48, 60, 72)
11 + 12 = 23 ✓
23 + 24 = 47 ✓
47 + 36 = 83 ✓
83 + 48 = 131 ✓
131 + 60 = 191 ✓
191 + 72 = 263 (expected)
But we have 251 instead of 263
251 ≠ 263, therefore 251 is the odd one out
The series follows the pattern: add (12n) where n = 1, 2, 3, 4, 5, 6
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