Number Series Questions with Answers: Quick Answer
These 20 number series questions are original practice questions written for this page. They are not previous year questions and are not copied from any book, test series or website. Every series was generated in code from a single stated rule, and the rule was checked to reproduce every given term and the answer exactly, so each series has exactly one fitting next term under its rule. The set covers the patterns SSC and bank exams actually use: squares and cubes, prime numbers, constant-ratio series, difference patterns, and alternating series. For each question, find the rule first, then the next term. As of 2 November 2026.
If you need the method before the questions, read the number series questions for SSC CGL note, the missing number series tricks for bank exams note and the wrong number series for bank exams note. The method box below is the minimum you need to attempt this set.
Number Series Methods: How to Find the Rule
Step 1 — Check the differences. If the first differences are constant, the rule is arithmetic. If the second differences are constant, the rule is quadratic (squares). If the differences themselves grow by a fixed amount, write them out as a second row.
Step 2 — Check the ratios. If each term is a fixed multiple of the previous one, the rule is geometric. Common multipliers in exams are 2, 3 and 1.5, often with a fixed number added or subtracted each step (×2 + 3, ×3 − 2, ×2 − 1).
Step 3 — Check squares, cubes and primes. Squares run 1, 4, 9, 16, 25, 36. Cubes run 1, 8, 27, 64, 125, 216. Primes run 2, 3, 5, 7, 11, 13, 17, 19. Many series are a square or cube plus or minus a fixed number.
Step 4 — Check alternating series. If the differences alternate in sign, split the series into odd and even positions and check each half separately.
| Pattern | Example in this set |
|---|---|
| Squares plus a constant | Q1, Q7 |
| Cubes plus or minus a constant | Q2, Q11, Q18 |
| Multiply and add or subtract | Q3, Q6, Q8, Q15 |
| Differences grow steadily | Q5, Q9, Q13, Q20 |
| Prime numbers | Q4 |
| Alternating steps | Q10 |
| Differences are squares | Q16 |
20 Number Series Questions with Answers and Solutions
Q1. 2, 5, 10, 17, 26, ?
(A) 35 (B) 36 (C) 37 (D) 38
Answer: (C) 37.
The terms are n² + 1: 1² + 1 = 2, 2² + 1 = 5, 3² + 1 = 10, 4² + 1 = 17, 5² + 1 = 26. Next is 6² + 1 = 37. The differences 3, 5, 7, 9 confirm it: the next difference is 11, and 26 + 11 = 37.
Q2. 0, 7, 26, 63, 124, ?
(A) 200 (B) 215 (C) 216 (D) 224
Answer: (B) 215.
The terms are n³ − 1: 1³ − 1 = 0, 2³ − 1 = 7, 3³ − 1 = 26, 4³ − 1 = 63, 5³ − 1 = 124. Next is 6³ − 1 = 216 − 1 = 215.
Q3. 5, 13, 29, 61, 125, ?
(A) 249 (B) 251 (C) 253 (D) 255
Answer: (C) 253.
Each term is double the previous term plus 3: 5 × 2 + 3 = 13, 13 × 2 + 3 = 29, 29 × 2 + 3 = 61, 61 × 2 + 3 = 125. Next is 125 × 2 + 3 = 253.
Q4. 2, 3, 5, 7, 11, 13, ?
(A) 15 (B) 17 (C) 19 (D) 21
Answer: (B) 17.
These are the prime numbers in order. The next prime after 13 is 17. The trap options 15 and 21 are odd but not prime.
Q5. 4, 10, 18, 28, 40, ?
(A) 52 (B) 54 (C) 56 (D) 50
Answer: (B) 54.
The differences are 6, 8, 10, 12, growing by 2 each time. The next difference is 14, so the next term is 40 + 14 = 54.
Q6. 7, 19, 55, 163, ?
(A) 487 (B) 485 (C) 489 (D) 491
Answer: (A) 487.
Each term is three times the previous term minus 2: 7 × 3 − 2 = 19, 19 × 3 − 2 = 55, 55 × 3 − 2 = 163. Next is 163 × 3 − 2 = 487.
Q7. 1, 4, 9, 16, 25, ?
(A) 30 (B) 32 (C) 36 (D) 49
Answer: (C) 36.
These are the squares 1², 2², 3², 4², 5². Next is 6² = 36. The differences 3, 5, 7, 9 confirm the square pattern.
Q8. 3, 5, 9, 17, 33, ?
(A) 63 (B) 64 (C) 65 (D) 66
Answer: (C) 65.
Each term is double the previous term minus 1: 3 × 2 − 1 = 5, 5 × 2 − 1 = 9, 9 × 2 − 1 = 17, 17 × 2 − 1 = 33. Next is 33 × 2 − 1 = 65.
Q9. 3, 6, 11, 18, 27, ?
(A) 36 (B) 38 (C) 40 (D) 37
Answer: (B) 38.
The differences are 3, 5, 7, 9 — the odd numbers in order. The next difference is 11, so the next term is 27 + 11 = 38.
Q10. 20, 25, 23, 28, 26, ?
(A) 29 (B) 31 (C) 33 (D) 30
Answer: (B) 31.
The steps alternate: +5, −2, +5, −2. After 26 comes a +5 step: 26 + 5 = 31. Splitting odd and even positions gives 20, 23, 26 and 25, 28, 31 — both rising by 3.
Q11. 3, 10, 29, 66, 127, ?
(A) 216 (B) 218 (C) 220 (D) 214
Answer: (B) 218.
The terms are n³ + 2: 1³ + 2 = 3, 2³ + 2 = 10, 3³ + 2 = 29, 4³ + 2 = 66, 5³ + 2 = 127. Next is 6³ + 2 = 218.
Q12. 8, 12, 18, 27, ?
(A) 36 (B) 38 (C) 40.5 (D) 45
Answer: (C) 40.5.
Each term is 1.5 times the previous term: 8 × 1.5 = 12, 12 × 1.5 = 18, 18 × 1.5 = 27. Next is 27 × 1.5 = 40.5. The differences 4, 6, 9 also grow by a factor of 1.5, which confirms the rule.
Q13. 15, 26, 39, 54, ?
(A) 69 (B) 71 (C) 73 (D) 67
Answer: (B) 71.
The differences are 11, 13, 15, growing by 2 each time. The next difference is 17, so the next term is 54 + 17 = 71.
Q14. 2, 6, 12, 20, 30, ?
(A) 40 (B) 42 (C) 44 (D) 36
Answer: (B) 42.
The terms are n × (n + 1): 1 × 2 = 2, 2 × 3 = 6, 3 × 4 = 12, 4 × 5 = 20, 5 × 6 = 30. Next is 6 × 7 = 42. The differences 4, 6, 8, 10 confirm it.
Q15. 6, 13, 27, 55, ?
(A) 109 (B) 111 (C) 110 (D) 113
Answer: (B) 111.
Each term is double the previous term plus 1: 6 × 2 + 1 = 13, 13 × 2 + 1 = 27, 27 × 2 + 1 = 55. Next is 55 × 2 + 1 = 111.
Q16. 5, 9, 18, 34, ?
(A) 55 (B) 57 (C) 59 (D) 61
Answer: (C) 59.
The differences are 4, 9, 16 — the squares 2², 3², 4². The next difference is 5² = 25, so the next term is 34 + 25 = 59.
Q17. 3, 6, 12, 24, ?
(A) 36 (B) 48 (C) 44 (D) 40
Answer: (B) 48.
Each term is double the previous term: 3 × 2 = 6, 6 × 2 = 12, 12 × 2 = 24. Next is 24 × 2 = 48.
Q18. 2, 10, 30, 68, 130, ?
(A) 220 (B) 222 (C) 224 (D) 218
Answer: (B) 222.
The terms are n³ + n: 1³ + 1 = 2, 2³ + 2 = 10, 3³ + 3 = 30, 4³ + 4 = 68, 5³ + 5 = 130. Next is 6³ + 6 = 222.
Q19. 4, 6, 10, 18, 34, ?
(A) 64 (B) 66 (C) 68 (D) 62
Answer: (B) 66.
The differences are 2, 4, 8, 16 — doubling each time. The next difference is 32, so the next term is 34 + 32 = 66.
Q20. 11, 14, 19, 26, 35, ?
(A) 44 (B) 46 (C) 48 (D) 45
Answer: (B) 46.
The differences are 3, 5, 7, 9 — the odd numbers in order. The next difference is 11, so the next term is 35 + 11 = 46.
Number Series Questions with Answers FAQs
How do you solve a number series question quickly?
Write the differences between consecutive terms as a second row. If that row is constant, arithmetic or geometric; if it grows steadily, it is a difference pattern; if the differences are squares or cubes, the rule is in the second row. Only then check squares, cubes and primes.
What are the most common number series patterns in SSC exams?
Squares and cubes with a constant added or subtracted, multiply-and-add rules (×2 + 1, ×3 − 2), difference patterns with differences growing by 2, and prime numbers. These four families cover most SSC CGL, CHSL and GD series questions.
What is the difference between a missing-number series and a wrong-number series?
In a missing-number series you find the next term from the rule. In a wrong-number series one given term breaks the rule and you must find it. The wrong number series for bank exams note practises the second form.
Why do two different rules sometimes seem to fit?
Short series can fit more than one rule. Use at least four given terms before trusting a rule, and prefer the simplest rule that fits every term. Every series on this page was checked in code to make sure its stated rule reproduces all given terms.
How many terms do you need to confirm a rule?
At least three steps of the rule, which means at least four given terms. With only two or three terms, several rules can fit, and the question is unfair. All 20 series here give four or more terms.