A series is a sequence of elements (numbers, letters, or symbols) arranged in a specific logical order, where the candidate must find the missing term or identify the wrong term based on the underlying pattern.
It checks:
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Observation skills
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Logical reasoning
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Pattern recognition
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Arithmetic ability
🔢 Types of Series
1️⃣ Number Series
A sequence of numbers following a mathematical pattern.
Common patterns:
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Addition/Subtraction
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Multiplication/Division
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Squares/Cubes
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Prime numbers
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Alternating patterns
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Fibonacci series
2️⃣ Alphabet Series
Letters arranged in a specific pattern based on their position in the alphabet.
Common rules:
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Position shifts (A→C, +2)
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Skipping letters
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Reverse order
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Alternate position change
3️⃣ Alphanumeric Series
A combination of letters and numbers (and sometimes symbols) with a logical pattern.
Example: A1, C3, E5, G7, ?
4️⃣ Mixed Series (Logic-Based)
Includes symbols, letters, and numbers — requires identifying a logical or positional pattern.
5️⃣ Wrong Number Series
All numbers follow a logic except one. You must spot the incorrect term.
🧠 Number Series – Key Patterns
| Pattern Type | Example | Explanation |
|---|---|---|
| + Constant | 2, 4, 6, 8, ? | Add 2 each time → 10 |
| – Constant | 15, 13, 11, ? | Subtract 2 → 9 |
| × Constant | 2, 4, 8, 16, ? | Multiply by 2 → 32 |
| ÷ Constant | 64, 32, 16, ? | Divide by 2 → 8 |
| Alternating | 1, 4, 2, 5, 3, ? | Add 3, –2 alternately → 6 |
| Squares | 1, 4, 9, 16, ? | Perfect squares → 25 |
| Cubes | 1, 8, 27, ? | Perfect cubes → 64 |
| Prime | 2, 3, 5, 7, ? | Next prime → 11 |
🔤 Alphabet Series – Key Concepts
| Series | Rule | Answer |
|---|---|---|
| A, C, E, G, ? | +2 | I |
| Z, X, V, T, ? | –2 | R |
| B, D, G, K, ? | +2, +3, +4 | P |
| A1, B2, C3, D4, ? | Sequential letters + numbers | E5 |
📘 Examples with Explanation
🟢 Example 1: Number Series
Q: 3, 6, 12, 24, ?
→ Multiply by 2 each step
✅ Answer: 48
🟢 Example 2: Missing Alphabet
Q: A, D, G, J, ?
→ +3 each step
✅ Answer: M
🟢 Example 3: Alphanumeric Series
Q: A1, C3, E5, G7, ?
→ Letters +2, Numbers +2
✅ Answer: I9
🟢 Example 4: Wrong Number
Q: 2, 4, 8, 16, 33, 64
Check: ×2 pattern
2×2 = 4, 4×2 = 8, 8×2 = 16, 16×2 = 32 (not 33)
✅ Answer: 33 is wrong
📝 Tips & Tricks
🔹 Memorize alphabet positions (A=1, Z=26)
🔹 Check first for +/– patterns, then ×/÷
🔹 Analyze alternate terms if direct pattern fails
🔹 Look out for square/cube roots
🔹 Eliminate options with logic when stuck
❓ Practice MCQs
🔸 Q1: What comes next?
5, 10, 20, 40, ?
a) 50
b) 60
c) 70
d) 80
→ Answer: d) 80
Pattern: ×2
🔸 Q2: Find the wrong number:
2, 6, 12, 20, 30, 42
→ Differences: +4, +6, +8, +10, +12
✅ All OK → No wrong number
🔸 Q3: What comes next in the series?
B, D, G, K, ?
a) L
b) N
c) M
d) O
→ Answer: d) O
Pattern: +2, +3, +4, +5 → +6 = O
📚 Common Series Patterns to Remember
| Type | Pattern | Example |
|---|---|---|
| Arithmetic | Constant addition/subtraction | 2, 4, 6, 8 |
| Geometric | Constant multiplication/division | 2, 4, 8, 16 |
| Alternating | Pattern alternates every term | 1, 2, 1, 2, ? |
| Square | Perfect squares | 1, 4, 9, 16 |
| Prime | Prime numbers | 2, 3, 5, 7, 11 |
| Composite | Non-prime numbers | 4, 6, 8, 9, 10 |
🧾 Summary
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Series questions test your ability to detect patterns and sequences
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Types include Number, Alphabet, Alphanumeric, and Mixed
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Focus on step-by-step logic
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Practice increases accuracy and speed
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