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SSC CGL Series Completion

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This page covers SSC CGL Series Completion with complete concept notes, 56 graded practice MCQs, key points and exam-specific tips. Free to study.

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Concept Notes

Series Completion— Rules & Concept

1.Core Concept

Read this first — the foundation of the topic

SERIES COMPLETION — SSC CGL VERBAL REASONING ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

CORE CONCEPT ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Series Completion means finding the missing or next term in a sequence. The sequence follows a hidden pattern. Your job is to find that pattern and apply it. The series can have numbers, letters, or both (alphanumeric). SSC CGL asks 3 to 5 questions from this subtopic in every paper. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

KEY RULES AND TYPES ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

1. NUMBER SERIES — Terms follow arithmetic, geometric, square, cube, or mixed patterns. 2. LETTER SERIES — Letters of the alphabet move forward or backward by a fixed or changing gap.

3. ALPHANUMERIC SERIES — A mix of letters and numbers. Each part follows its own rule. 4. DIFFERENCE SERIES — The difference between terms increases or decreases in a pattern.

5. TWO-TIER DIFFERENCE SERIES — The difference of differences forms a pattern (second-order difference). ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

2.Formula Block

Memorise — at least one formula appears in every paper
• Arithmetic Series: Each term = Previous term + Fixed number (common difference d)
Formula: Nth term = a + (n-1) x d
• Geometric Series: Each term = Previous term x Fixed number (common ratio r)
Formula: Nth term = a x r^(n-1)
• Alphabet Position: A=1, B=2, C=3 ... Z=26. Remember: EJOTY shortcut (E=5, J=10, O=15, T=20, Y=25)

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

• Square Series: Terms are 1, 4, 9, 16, 25, 36... (n squared)

• Cube Series: Terms are 1, 8, 27, 64, 125... (n cubed)

• Prime Series: 2, 3, 5, 7, 11, 13, 17, 19, 23...

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

3.Exam Patterns

What examiners ask — read before attempting PYQs

— WHAT GETS ASKED ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ • Find the next term: 2, 6, 12, 20, 30, ? • Find the missing term: 3, 7, ?, 21, 31 • Find the wrong term: 1, 4, 9, 16, 24, 36 • Letter series: ABD, CFI, EHN, ? • Mixed pattern series: A2, C4, E8, G16, ? ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

4.Shortcuts

Use these to save 30–60 seconds per question
Example

2, 6, 12, 20, 30 → Differences: 4, 6, 8, 10 → Next difference = 12 → Next term = 30 + 12 = 42 TRICK 2 — EJOTY ALPHABET TRICK Memorize: E=5, J=10, O=15, T=20, Y=25. Use this to instantly find the position of any letter without counting from A. For example, if the question has letter R, R comes after O(15), so R = 15+3 = 18. TRICK 3 — SPLIT AND SOLVE FOR ALPHANUMERIC In alphanumeric series, always separate letters and numbers. Solve them independently.

Then combine the answers

Example

A2, C4, E8, G16 → Letters: A, C, E, G (gap of 2 each time) → Next letter: I

Numbers

2, 4, 8, 16 (multiplied by 2 each time) → Next number: 32 → Answer: I32 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

5.Worked Example

Solve this step-by-step before moving on
1
Step 1

Check the terms — 1=1², 4=2², 9=3², 16=4², 25=5²

2
Step 2

Pattern is squares of natural numbers.

3
Step 3

Next term = 6² = 36 Answer: 36 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ WORKED EXAMPLE 2 — LETTER SERIES ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Question: Find the next term: BEH, KNQ, TWZ, ?

1
Step 1

Look at each group — B(2), E(5), H(8). Gap between letters in group = 3.

2
Step 2

Gap between first letters of groups: B(2) → K(11) → T(20). Gap = 9 each time.

3
Step 3

Next first letter = T(20) + 9 = 29. But Z=26, so count ahead: 20+9=29, 29-26=3, that is letter C.

4
Step 4

Apply gap of 3 within group: C(3), F(6), I(9) Answer: CFI ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

6.Exam Traps

Common mistakes students make — avoid these

— NUMBER 1 TRAP ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Students confuse ADDITION patterns with MULTIPLICATION patterns when numbers grow fast. Always check BOTH. For series like 3, 6, 12, 24 — the difference is also increasing (3, 6, 12) but the real pattern is x2 each time.

Always try multiplication first if differences are themselves doubling. This trap catches nearly 40% of students in mock tests.

Key Points to Remember

  • Series Completion asks you to find the next, missing, or wrong term in a number, letter, or alphanumeric sequence.
  • Always write differences between consecutive terms first — this single step solves 60% of number series questions.
  • EJOTY Trick: E=5, J=10, O=15, T=20, Y=25 — use this to find any letter's position instantly without counting.
  • Arithmetic Series Formula: Nth term = a + (n-1) x d, where a is first term and d is common difference.
  • Geometric Series Formula: Nth term = a x r^(n-1), where r is the common ratio (multiplication factor).
  • For alphanumeric series, always split letters and numbers, solve each part separately, then combine.
  • If first-level differences are not equal, find second-level differences (difference of differences) — this reveals hidden patterns.
  • Square series pattern: 1, 4, 9, 16, 25, 36... Cube series pattern: 1, 8, 27, 64, 125... Memorise both up to 20.
  • Prime number series: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29 — gaps are not fixed, so learn these by heart.
  • When numbers grow very fast (doubling or tripling), suspect a geometric (multiplication) pattern, not an addition pattern.

Exam-Specific Tips

  • The EJOTY rule assigns positions E=5, J=10, O=15, T=20, Y=25 and is the fastest way to decode letter series in SSC exams.
  • In SSC CGL Tier 1, Series Completion typically contributes 3 to 5 questions out of 25 questions in the Reasoning section.
  • A second-order difference series is one where the differences between terms are not equal, but the differences OF those differences are equal — this pattern appears frequently in SSC CGL.
  • The sum of first n natural numbers formula is n x (n+1) / 2 — series like 1, 3, 6, 10, 15 are based on this formula.
  • Fibonacci series rule: each term = sum of the two terms before it (1, 1, 2, 3, 5, 8, 13, 21...) — SSC occasionally tests this.
  • In a letter series, the total number of letters in the English alphabet is 26 — when position exceeds 26, subtract 26 to cycle back.
  • The square of numbers 1 to 20 and cubes of numbers 1 to 10 are directly tested in SSC CGL number series questions and must be memorised.
Practice MCQs

Series Completion — Practice Questions

56graded MCQs · easy to hard · full solution & trap analysis · showing 20 of 56

All MCQs →
Practice 1easy

Find the missing number: 2, 3, 5, 7, 11, 13, ?

Practice 2easy

What comes next in the series: 2, 3, 5, 7, 11, 13, ?

Practice 3easy

Complete the series: 5, 10, 20, 40, 80, ?

Practice 4easy

Complete the series: 3, 6, 12, 24, 48, ?

Practice 5easy

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

Practice 6easy

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

Practice 7easy

Find the missing term in the series: 2, 5, 10, 17, 26, ?

Practice 8easy

Find the next term: 1, 4, 9, 16, 25, ?

Practice 9easy

Complete the series: 3, 6, 12, 24, 48, ?

Practice 10easy

Find the missing term in the series: 3, 6, 12, 24, 48, ?

Practice 11easy

Find the missing term in the series: 3, 6, 12, 24, 48, ?

Practice 12easy

Find the missing term in the series: 2, 5, 10, 17, 26, ?

Practice 13easy

What comes next? 2, 3, 5, 7, 11, 13, ?

Practice 14easy

Find the missing number: 5, 8, 13, 20, 29, ?

Practice 15easy

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

Practice 16easy

What comes next in the series: 2, 3, 5, 7, 11, 13, ?

Practice 17easy

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

Practice 18easy

Find the missing term in the series: 3, 6, 9, 12, ?, 18

Practice 19medium

What is the next term in the series: 5, 11, 23, 47, 95, ?

Practice 20medium

What comes next? 2, 3, 5, 8, 13, 21, ?, 55

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60-Second Revision — Series Completion

  • Remember: Always find differences between terms first — if equal, it is arithmetic; if differences grow equally, it is second-order.
  • Trick: Use EJOTY (E=5, J=10, O=15, T=20, Y=25) to find letter positions in under 3 seconds.
  • Formula: Nth term of arithmetic series = a + (n-1) x d. Nth term of geometric series = a x r^(n-1).
  • Trap: Do NOT assume addition when numbers grow fast — check multiplication (geometric) pattern first when differences are doubling.
  • Remember: For alphanumeric series, always split letters and numbers, solve separately, then combine into one answer.
  • Memorise squares up to 20 and cubes up to 10 before the exam — at least 1 question per paper is directly based on these.
  • Trap: In letter series that wrap around Z, subtract 26 from the position — students lose easy marks by forgetting alphabet cycling.
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