1
What comes next: 4, 11, 18, 25, ___?
Correct answer: D. 32
Each term increases by 7: 4 + 7 = 11, 11 + 7 = 18, 18 + 7 = 25, so the next term is 25 + 7 = 32. This is an arithmetic sequence with common difference 7.
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Number Series Practice MCQs
Civil Service Exam numerical ability reviewer with number series built on differences, ratios, squares, cubes, primes, Fibonacci and alternating rules, each with the rule explained.
20 MCQsUpdated 3 November 2026
Number sequence is one of the three items in the official Numerical Ability scope of the Civil Service Exam. This practice set covers every common pattern: constant and growing differences, multiplication and division, squares and cubes with or without a constant, primes, triangular and Fibonacci numbers, and alternating two-step rules, including finding a missing middle term.
Work through the checklist in order: differences, then ratios, then squares and cubes, then two-term sums and alternating rules. Every series here was checked by script against its stated rule.
- 2
What comes next: 2, 6, 18, 54, ___?
Correct answer: A. 162
Each term is three times the previous one: 2 × 3 = 6, 6 × 3 = 18, 18 × 3 = 54, so the next is 54 × 3 = 162. This is a geometric sequence with ratio 3.
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What comes next: 1, 2, 4, 7, 11, ___?
Correct answer: A. 16
The differences are 1, 2, 3 and 4, increasing by one, so the next difference is 5: 11 + 5 = 16.
easy - 4
What comes next: 1, 8, 27, 64, ___?
Correct answer: D. 125
These are the cubes 1³, 2³, 3³ and 4³, so the next term is 5³ = 125. Learning the cubes up to 10³ makes such series easy to recognise.
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What comes next: 3, 5, 9, 17, 33, ___?
Correct answer: C. 65
Each term is double the previous term minus 1: 3 × 2 − 1 = 5, 5 × 2 − 1 = 9, and so on, so 33 × 2 − 1 = 65. The differences 2, 4, 8, 16 also double each time.
Read detailsmedium - 6
What comes next: 2, 5, 10, 17, 26, ___?
Correct answer: A. 37
Each term is a perfect square plus 1: 1²+1 = 2, 2²+1 = 5, 3²+1 = 10, 4²+1 = 17, 5²+1 = 26, so the next is 6²+1 = 37.
medium - 7
What comes next: 1, 1, 2, 3, 5, 8, ___?
Correct answer: D. 13
This is the Fibonacci sequence: each term is the sum of the two before it. 5 + 8 = 13.
easy - 8
What comes next: 64, 32, 16, 8, ___?
Correct answer: A. 4
Each term is half of the previous one: 64 ÷ 2 = 32, and so on, so 8 ÷ 2 = 4.
easy - 9
What comes next: 5, 10, 8, 16, 14, 28, ___?
Correct answer: B. 26
The rule alternates: × 2, then − 2. 5 × 2 = 10, 10 − 2 = 8, 8 × 2 = 16, 16 − 2 = 14, 14 × 2 = 28, so the next step is 28 − 2 = 26.
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Find the missing term: 3, 7, ___, 15, 19
Correct answer: C. 11
The terms increase by 4 each time: 3, 7, 11, 15, 19. The missing term is 7 + 4 = 11, and 11 + 4 = 15 confirms it.
easy - 11
Find the missing term: 2, 4, 12, ___, 240
Correct answer: D. 48
The multipliers increase by one each time: × 2, × 3, × 4, × 5. So 12 × 4 = 48, and 48 × 5 = 240 confirms the pattern.
hard - 12
What comes next: 100, 91, 83, 76, 70, ___?
Correct answer: A. 65
The differences are −9, −8, −7 and −6, shrinking by one each time, so the next difference is −5: 70 − 5 = 65.
medium - 13
What comes next: 1, 3, 6, 10, 15, ___?
Correct answer: C. 21
These are triangular numbers: add 2, 3, 4, 5 and then 6. So 15 + 6 = 21.
easy - 14
What comes next: 7, 14, 28, 56, ___?
Correct answer: D. 112
Each term doubles: 56 × 2 = 112. It is also 7 × 1, 7 × 2, 7 × 4, 7 × 8, so the next is 7 × 16 = 112.
easy - 15
What comes next: 11, 13, 17, 19, 23, ___?
Correct answer: A. 29
These are consecutive prime numbers. After 23, the next prime is 29, since 24, 25, 26, 27 and 28 all have other factors.
Read detailsmedium - 16
Find the missing term: 81, ___, 49, 36, 25
Correct answer: C. 64
These are perfect squares in decreasing order: 9², 8², 7², 6², 5². The missing term is 8² = 64.
easy - 17
What comes next: 1, 4, 13, 40, ___?
Correct answer: C. 121
Each term is three times the previous one plus 1: 1 × 3 + 1 = 4, 4 × 3 + 1 = 13, 13 × 3 + 1 = 40, so 40 × 3 + 1 = 121.
hard - 18
What comes next: 20, 18, 21, 19, 22, 20, ___?
Correct answer: A. 23
The rule alternates: − 2, then + 3. 20 − 2 = 18, 18 + 3 = 21, 21 − 2 = 19, 19 + 3 = 22, 22 − 2 = 20, so the next is 20 + 3 = 23.
Read detailshard - 19
What comes next: 0, 3, 8, 15, 24, ___?
Correct answer: D. 35
Each term is one less than a perfect square: 1−1, 4−1, 9−1, 16−1, 25−1. The next is 36 − 1 = 35. The differences 3, 5, 7, 9, 11 also confirm it.
Read detailsmedium - 20
What comes next: 6, 12, 10, 20, 18, ___?
Correct answer: A. 36
The rule alternates: × 2, then − 2. 6 × 2 = 12, 12 − 2 = 10, 10 × 2 = 20, 20 − 2 = 18, so the next step is 18 × 2 = 36.
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