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SSC CGL Preparation – Day 3
Reasoning – Series Completion
✅ What is Series Completion?
In Series Completion, you are given a sequence of numbers, letters, or figures arranged in a particular pattern. Your task is to identify the missing element or predict the next one based on the logic or rule of the series.
📚 Types of Series Questions in SSC CGL
🔢 1. Number Series
Series where numbers follow a certain rule based on:
- Addition/Subtraction
- Multiplication/Division
- Squares/Cubes
- Prime Numbers
- Fibonacci Series
- Alternating Pattern
Example:
2, 4, 8, 16, ?
Solution: Each number is ×2 → Answer = 32
🔤 2. Alphabet Series
Series based on alphabetical position, skip patterns, reverse order, etc.
Example:
A, D, G, J, ?
Solution: Each letter is +3 → A(1), D(4), G(7), J(10) → Next: M(13) = M
🔁 3. Alphanumeric Series
Series involving a combination of letters and numbers. May also include symbols.
Example:
A1, B2, C3, D4, ?
Solution: Pattern is sequential letters with matching digits → Answer: E5
🧩 4. Mixed Series
Series combining patterns, alternating sequences, or logical reasoning.
Example:
1, 4, 9, 16, ?, 36
Solution: Squares of natural numbers → 1², 2², 3²… → Missing: 25 (5²)
🔺 5. Figure/Pattern Series (Non-Verbal)
A sequence of figures where you must choose the one that completes or follows the pattern.
Example: Rotating shapes, increasing dots, alternate shading, etc.
🧠 Key Concepts to Master
✅ Common Patterns
- Arithmetic (+/−)
- Geometric (×/÷)
- Difference of differences
- Odd/Even placement
- Alternating sequences
- Squares and cubes
- Prime numbers
✅ Alphabet Positions
A = 1, B = 2, …, Z = 26
Reverse: A = 26, …, Z = 1
Useful for computing letter patterns quickly.
✅ Tip: Memorize Prime Numbers till 100
Helps quickly spot prime-related series.
🎯 Strategy for Solving Series
- Observe the pattern carefully.
- Calculate differences between terms.
- Check if a square, cube, or prime pattern exists.
- Watch for alternating or repeating sequences.
- Use elimination for options when stuck.
🧮 Formulas and Tricks
| Pattern Type | Example | Rule |
|---|---|---|
| + Constant | 3, 6, 9, 12 | +3 |
| × Constant | 2, 4, 8, 16 | ×2 |
| Squares | 1, 4, 9, 16 | n² |
| Cubes | 1, 8, 27 | n³ |
| Alternating | 1, 2, 4, 3, 7, 4 | (+1, +2), alternate |
| Alphabet | A, D, G, J | +3 |
⚠️ SSC CGL Exam Tip
- 3–4 questions usually come from Series Completion.
- Focus on Number and Alphanumeric Series.
- Time limit per question: 40–60 seconds.
📖 Examples with Explanation
Example 1:
Find the next number:
5, 11, 17, 23, ?
Solution:
Each term increases by 6
Answer: 29 ✅
Example 2:
Find the missing term:
Z, X, V, T, ?
Solution:
Reverse Alphabet Series: Z(26), X(24), V(22), T(20) → Next: R (18) ✅
Example 3:
Find the next in series:
1, 4, 9, 16, ?, 36
Solution:
Squares: 1², 2², 3², 4², ?, 6² → 5² = 25 ✅
🛠️ Practice Suggestions
- Solve 20 questions from each type.
- Focus on speed + accuracy.
- Mix verbal & non-verbal practice once you’re confident.
