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RRB Group D Number Series

Study Material — 3 PYQs (2021–2021) · Concept Notes · Shortcuts

RRB Group D Number Series is a frequently tested subtopic — 3 previous year questions from 2021–2021 papers are included below with concept notes, key rules and shortcut tricks.

3 PYQs
2021–2021
2 Practice
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8 Key Points
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Previous Year Questions

RRB Group D Number Series — Past Exam Questions

3 questions from actual RRB Group D papers · all shown free · click option to reveal solution

Exam Q 12021Previous Year Pattern

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?

Exam Q 22021Previous Year Pattern

In a number series, the nth term is given by the formula: aₙ = n² + 2n − 1. What is the difference between the 5th term and the 3rd term?

Exam Q 32021Previous Year Pattern

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 6, what is the 6th term?

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

2graded MCQs · easy to hard · full solution & trap analysis

All MCQs →
Practice 1easy

Study the following number series and find the missing term: 2, 6, 12, 20, 30, ? What is the next number in the series?

Practice 2hard

In a number series, the first term is 3. Each subsequent term is formed by multiplying the previous term by 2 and then subtracting 1. What is the 6th term of this series?

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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