Study Material — 17 PYQs (2019–2019) · Concept Notes · Shortcuts
SSC CPO Number Series is a frequently tested subtopic — 17 previous year questions from 2019–2019 papers are included below with concept notes, key rules and shortcut tricks.
17 questions from actual SSC CPO papers · all shown free · click option to reveal solution
Exam Q 12019Previous Year Pattern
Find the next number in the series: 2, 6, 12, 20, 30, ?
Exam Q 22019Previous Year Pattern
What is the missing number in the series: 5, 10, 20, 40, ?, 160?
Exam Q 32019Previous Year Pattern
Find the next term in the series: 1, 1, 2, 3, 5, 8, 13, ?
Exam Q 42019Previous Year Pattern
What is the next term in the series: 3, 9, 27, 81, ?
Exam Q 52019Previous Year Pattern
Find the missing number in the series: 2, 8, 18, 32, 50, ?
Exam Q 62019Previous Year Pattern
What is the next number in the series: 100, 99, 97, 94, 90, ?
Exam Q 72019Previous 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 82019Previous Year Pattern
A series has the property that each term is the sum of the two preceding terms. If the 3rd term is 5 and the 4th term is 8, what is the 1st term?
Exam Q 92019Previous Year Pattern
In a number series, the sum of the first n terms is given by Sₙ = n² + 2n. What is the 4th term of the series?
Exam Q 102019Previous Year Pattern
A series is defined as: a₁ = 10, and aₙ = aₙ₋₁ + 2n for n ≥ 2. Find a₅.
Exam Q 112019Previous Year Pattern
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?
Exam Q 122019Previous Year Pattern
A number series follows the pattern: 3, 6, 12, 24, 48, ... What is the 8th term?
Exam Q 132019Previous Year Pattern
A series has terms where aₙ = (n³ - n)/3 for positive integers n. Which of the following is NOT a term in this series?
Exam Q 142019Previous Year Pattern
In a number series, the first term is 2 and each subsequent term is obtained by multiplying the previous term by 3 and then subtracting 1. What is the 5th term of this series?
Exam Q 152019Previous Year Pattern
A series is defined as: a₁ = 3, and aₙ = aₙ₋₁² - 2aₙ₋₁ for n ≥ 2. Find a₄.
Exam Q 162019Previous Year Pattern
In a series, aₙ = aₙ₋₁ + aₙ₋₂ (Fibonacci-like), with a₁ = 2 and a₂ = 3. What is the sum of the first 7 terms?
Exam Q 172019Previous Year Pattern
In a series, the difference between consecutive terms follows a pattern: 1st difference is 2, 2nd difference is 5, 3rd difference is 10, 4th difference is 17. If the first term is 5, what is the 5th 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
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