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RRB NTPC Number Series

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This page covers RRB NTPC Number Series with complete concept notes, 42 graded practice MCQs, key points and exam-specific tips. Free to study.

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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

42graded MCQs · easy to hard · full solution & trap analysis · showing 20 of 42

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Practice 1easy

Complete the series: 1, 4, 9, 16, 25, ?, 49

Practice 2easy

What comes next? 2, 5, 10, 17, 26, ?

Practice 3easy

What is the next number in the series: 3, 9, 27, 81, ?

Practice 4easy

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

Practice 5easy

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

Practice 6easy

Find the missing number in the series: 2, 6, 12, 20, 30, ?, 56

Practice 7easy

Find the next number: 100, 50, 25, 12.5, ?

Practice 8easy

What is the next number in the series: 1, 4, 9, 16, 25, ?

Practice 9easy

Complete the series: 1, 4, 9, 16, 25, ___

Practice 10easy

Find the missing term: 3, 9, 27, 81, ?

Practice 11easy

Find the next number in the series: 100, 50, 25, 12.5, ___

Practice 12easy

Find the missing number: 3, 8, 15, 24, 35, ___

Practice 13easy

What is the next term in the series: 5, 10, 20, 40, 80, ___?

Practice 14easy

Find the missing number in the series: 2, 6, 12, 20, 30, ___

Practice 15easy

Find the missing term: 5, 10, 20, 40, 80, ?

Practice 16easy

What is the next term in the series: 2, 6, 12, 20, 30, ?

Practice 17medium

In a series, the difference between consecutive terms increases by 1 each time. If the first term is 2 and the second term is 3, what is the 6th term?

Practice 18medium

A series is constructed where each term is the product of its position and the sum of all previous terms. If the first term is 2, what is the 4th term?

Practice 19medium

In a series, the difference between consecutive terms increases by 1 each time. If the first term is 3 and the second term is 4, what is the 6th term?

Practice 20medium

A series is defined as: 2, 6, 12, 20, 30, ... What is the 8th 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
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