MCQs / Quantitative Reasoning / Number Series

Number Series MCQs — Quantitative Reasoning

42 multiple-choice questions on Number Series from Quantitative Reasoning, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

1. Find the next number in the series: 25, 36, 49, 64, 81, ?

  1. 100
  2. 98
  3. 94
  4. 106

Answer: A) 100

Explanation: The terms are n^2 for n = 5, 6, dots — next is 10^2 = 100.

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2. Find the next number in the series: 5, 20, 80, 320, 1280, ?

  1. 5123
  2. 5120
  3. 2240
  4. 5115

Answer: B) 5120

Explanation: Each term is multiplied by 4: 1280 4 = 5120.

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3. Find the next number in the series: 3, 8, 15, 24, 35, ?

  1. 46
  2. 48
  3. 52
  4. 47

Answer: B) 48

Explanation: The terms are n^2-1 for n = 2, 3, dots — next is 7^2-1 = 48.

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4. Find the next number in the series: 50, 1, 45, 5, 40, 9, ?

  1. 35
  2. 29
  3. 13
  4. 39

Answer: A) 35

Explanation: Two series are mixed together. Odd positions: 50, 45, 40 (step -5); even positions: 1, 5, 9 (step 4). Next is an odd position: 40 - 5 = 35.

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5. Find the next number in the series: 7, 21, 63, 189, 567, ?

  1. 1701
  2. 1707
  3. 1699
  4. 945

Answer: A) 1701

Explanation: Each term is multiplied by 3: 567 3 = 1701.

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6. Find the next number in the series: 10, 3, 20, 6, 30, 9, ?

  1. 34
  2. 40
  3. 12
  4. 45

Answer: B) 40

Explanation: Two series are mixed together. Odd positions: 10, 20, 30 (step 10); even positions: 3, 6, 9 (step 3). Next is an odd position: 30 + 10 = 40.

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7. Find the next number in the series: 5, 8, 14, 23, 35, ?

  1. 50
  2. 56
  3. 55
  4. 47

Answer: A) 50

Explanation: Differences are 3, 6, 9, 12 — they change by 3 each time, so the next difference is 15: 35 + 15 = 50.

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8. Find the missing number: 4, 9, 16, ?, 36, 49

  1. 27
  2. 29
  3. 22
  4. 25

Answer: D) 25

Explanation: Perfect squares 2^2, 3^2, dots, 7^2; missing 5^2 = 25.

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9. Find the next number in the series: 11, 13, 17, 19, 23, ?

  1. 25
  2. 27
  3. 31
  4. 29

Answer: D) 29

Explanation: Consecutive primes; after 23 comes 29 (25 and 27 are not prime).

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10. Find the next number in the series: 1, 1, 2, 3, 5, 8, ?

  1. 17
  2. 11
  3. 13
  4. 16

Answer: C) 13

Explanation: Each term is the sum of the two before it: 5 + 8 = 13.

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11. Find the next number in the series: 2, 20, 5, 18, 8, 16, ?

  1. 16
  2. 11
  3. 12
  4. 14

Answer: B) 11

Explanation: Two series are mixed together. Odd positions: 2, 5, 8 (step 3); even positions: 20, 18, 16 (step -2). Next is an odd position: 8 + 3 = 11.

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12. Find the missing number: 81, ?, 9, 3, 1

  1. 30
  2. 22
  3. 31
  4. 27

Answer: D) 27

Explanation: Each term is divided by 3; missing 81 div 3 = 27.

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13. Find the next number in the series: 2, 5, 14, 41, 122, ?

  1. 366
  2. 369
  3. 365
  4. 370

Answer: C) 365

Explanation: Rule: multiply by 3 then subtract 1. 122 3 - 1 = 365.

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14. Find the next number in the series: 1, 4, 9, 16, 25, ?

  1. 38
  2. 30
  3. 36
  4. 37

Answer: C) 36

Explanation: The terms are n^2 for n = 1, 2, dots — next is 6^2 = 36.

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15. Find the next number in the series: 3, 6, 12, 24, 48, ?

  1. 97
  2. 96
  3. 102
  4. 72

Answer: B) 96

Explanation: Each term is multiplied by 2: 48 2 = 96.

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16. Find the next number in the series: 4, 19, 34, 49, 64, ?

  1. 78
  2. 79
  3. 85
  4. 84

Answer: B) 79

Explanation: Each term increases by 15: 64 + 15 = 79.

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17. Find the next number in the series: 3, 8, 18, 38, 78, ?

  1. 156
  2. 164
  3. 152
  4. 158

Answer: D) 158

Explanation: Rule: multiply by 2 then add 2. 78 2 + 2 = 158.

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18. Find the next number in the series: 1, 3, 7, 15, 31, ?

  1. 62
  2. 63
  3. 57
  4. 74

Answer: B) 63

Explanation: Rule: multiply by 2 then add 1. 31 2 + 1 = 63.

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19. Find the missing number: 1, 4, 9, 16, ?, 36

  1. 22
  2. 20
  3. 29
  4. 25

Answer: D) 25

Explanation: Squares of 1 to 6; missing 5^2 = 25.

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20. Find the next number in the series: 2, 3, 5, 7, 11, ?

  1. 13
  2. 15
  3. 17
  4. 12

Answer: A) 13

Explanation: These are prime numbers; the prime after 11 is 13.

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21. Find the missing number: 3, 6, ?, 24, 48, 96

  1. 18
  2. 12
  3. 13
  4. 10

Answer: B) 12

Explanation: Each term doubles; missing 6 2 = 12.

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22. Find the next number in the series: 3, 4, 7, 11, 18, 29, ?

  1. 40
  2. 47
  3. 49
  4. 58

Answer: B) 47

Explanation: Each term is the sum of the two before it: 18 + 29 = 47.

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23. Find the next number in the series: 100, 98, 93, 85, 74, ?

  1. 55
  2. 61
  3. 63
  4. 60

Answer: D) 60

Explanation: Differences are -2, -5, -8, -11 — they change by -3 each time, so the next difference is -14: 74 - 14 = 60.

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24. Find the next number in the series: 13, 22, 31, 40, 49, ?

  1. 58
  2. 56
  3. 53
  4. 62

Answer: A) 58

Explanation: Each term increases by 9: 49 + 9 = 58.

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25. Find the next number in the series: 1, 8, 27, 64, 125, ?

  1. 211
  2. 196
  3. 180
  4. 216

Answer: D) 216

Explanation: The terms are cubes: 1^3, 2^3, dots, 5^3, so next is 6^3 = 216.

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