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SSC CHSL Number Series

Study Material — 1 PYQs (2018–2018) · Concept Notes · Shortcuts

SSC CHSL Number Series is a frequently tested subtopic — 1 previous year questions from 2018–2018 papers are included below with concept notes, key rules and shortcut tricks.

1 PYQs
2018–2018
27 Practice
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8 Key Points
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Previous Year Questions

SSC CHSL Number Series — Past Exam Questions

1 questions from actual SSC CHSL papers · all shown free · click option to reveal solution

Exam Q 12018Previous Year Pattern

Find the missing number in the series: 2, 6, 18, 54, ?

Concept Notes

Number Series— Rules & Concept

Core ConceptRead this first — the foundation of the topic
Arithmetic Series

Each term increases or decreases by a constant difference

Example

5, 8, 11, 14 (difference = +3) 2

Geometric Series

Each term is multiplied by a constant ratio

Example

2, 6, 18, 54 (ratio = ×3) 3. Square/Cube Series: Based on squares or cubes of consecutive numbers

Example

1, 4, 9, 16 (1², 2², 3², 4²) 4

Prime Number Series

Following prime number sequence 5

Mixed Operations

Combination of addition, subtraction, multiplication, division 6. Double/Triple Layer Series: Two or three different patterns running simultaneously

Exam PatternsWhat examiners ask — read before attempting PYQs

SSC CGL typically asks 2-3 questions on number series. Common question types include finding the missing term, identifying the wrong number, or completing the series. The difficulty ranges from simple arithmetic progressions to complex mixed operation patterns. Powerful Shortcut - The Difference Method: Write differences between consecutive terms. If first-level differences don't show pattern, find second-level differences (differences of differences).

Most SSC series get solved within 2-3 levels.

Worked ExampleSolve this step-by-step before moving on
1
Step 1

Find first-level differences 7-3 = 4 15-7 = 8 31-15 = 16 ? -31 = ? 127-? = ?

2
Step 2

Observe the difference pattern 4, 8, 16, ?, ? This is a geometric series with ratio 2 Next difference = 16 × 2 = 32 Following difference = 32 × 2 = 64

3
Step 3

Find the missing number ? = 31 + 32 = 63 Verify: 127 - 63 = 64 ✓ Answer: 63

ShortcutsUse these to save 30–60 seconds per question

for Square Series: If you see numbers like 2, 5, 10, 17, 26, check if they follow n² + 1 pattern: 1² + 1 = 2 2² + 1 = 5 3² + 1 = 10 4² + 1 = 17 5² + 1 = 26

Exam TrapsCommon mistakes students make — avoid these

Students often assume the first pattern they see is correct. Always verify your answer by checking if it fits the complete series. In mixed operation series, don't stop at first-level differences - go deeper if needed.

Key Points to Remember

  • Number series questions appear 2-3 times in SSC CGL with moderate to high difficulty
  • Use difference method: find differences between consecutive terms to identify pattern
  • Arithmetic series have constant difference, geometric series have constant ratio
  • Square series follow pattern n², n²+1, n²-1, or similar variations
  • Prime number series: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29...
  • Mixed operation series combine addition, subtraction, multiplication, division patterns
  • Double layer series have two different patterns running simultaneously
  • Always verify your answer by checking if it satisfies the complete series pattern

Exam-Specific Tips

  • First 10 prime numbers: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29
  • Perfect squares up to 15²: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225
  • Perfect cubes up to 10³: 1, 8, 27, 64, 125, 216, 343, 512, 729, 1000
  • Fibonacci series starts: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89
  • Common ratios in geometric series: ×2, ×3, ×0.5, ×1.5, ×4
  • Triangular numbers: 1, 3, 6, 10, 15, 21, 28, 36, 45, 55
  • Powers of 2: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024
  • Most SSC number series can be solved using maximum 3 levels of differences
Practice MCQs

Number Series — Practice Questions

27graded MCQs · easy to hard · full solution & trap analysis · showing 20 of 27

All MCQs →
Practice 1easy

What is the next term in the series: 3, 6, 12, 24, 48, ?

Practice 2easy

Find the missing number: 2, 4, 8, 16, 32, ?

Practice 3easy

Find the next number in the series: 2, 6, 12, 20, 30, ?

Practice 4easy

What is the missing number in the series: 5, 10, 20, 40, 80, ?

Practice 5easy

Complete the series: 1, 3, 9, 27, 81, ?

Practice 6easy

Complete the series: 1, 4, 9, 16, 25, 36, ?

Practice 7easy

Find the next term: 3, 6, 12, 24, 48, ?

Practice 8easy

What comes next in the series: 2, 3, 5, 8, 13, 21, ?

Practice 9easy

Identify the next number: 100, 90, 81, 73, 66, ?

Practice 10easy

Find the missing number in the series: 5, 10, 20, 40, 80, ?

Practice 11medium

A number series follows the pattern where the difference between consecutive terms increases by 2 each time. If the first term is 3 and the second term is 5, what is the 6th term?

Practice 12medium

In a geometric series, the 2nd term is 6 and the 4th term is 54. What is the 1st term?

Practice 13medium

In a number series, the first term is 5 and each subsequent term is obtained by multiplying the previous term by 2 and then subtracting 3. What is the 5th term of this series?

Practice 14medium

In a series, each term is the sum of the two preceding terms. If the 3rd term is 8 and the 4th term is 13, what is the 1st term?

Practice 15medium

A series is defined as: T(n) = n² + 2n + 1. What is the difference between the 7th term and the 5th term?

Practice 16medium

A series has the property that T(n) = T(n−1) + T(n−2) for n ≥ 3. If T(4) = 7 and T(5) = 11, what is T(2)?

Practice 17medium

A number series follows the pattern: 3, 6, 12, 24, ?, 96. What is the missing number?

Practice 18medium

A series is defined as: T(n) = n² + 2n. What is the sum of the 3rd and 5th terms?

Practice 19medium

In a series, the difference between consecutive terms increases by 1 each time. The series starts: 2, 3, 5, 8, 12, ?. What is the next term?

Practice 20hard

A series is constructed as follows: start with 2, then each subsequent term is the sum of all previous terms plus 1. What is the 6th term of this series?

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60-Second Revision — Number Series

  • Remember: Apply difference method first - find differences between consecutive terms
  • Formula: For arithmetic series, nth term = a + (n-1)d where a=first term, d=common difference
  • Trick: If first differences don't work, try second-level differences immediately
  • Pattern: Check for squares (n²), cubes (n³), or modified versions (n²±k)
  • Trap: Don't assume first pattern you see is correct - always verify with complete series
  • Speed: Memorize first 15 squares, 10 cubes, and 10 prime numbers
  • Strategy: For geometric series, check if ratio is consistent throughout the sequence
←Divisibility RulesFractions & Decimals→
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