SSC CGL Preparation – Day 12

Reasoning: Series Completion

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📘 What is Series Completion?

A series is a sequence of terms (numbers, letters, or a combination) following a specific pattern or logic. Your task is to identify the rule and find the missing term or next item in the sequence.

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🔍 Types of Series:

1. Number Series

A series made of numbers with logical patterns such as:

• Addition/Subtraction
• Multiplication/Division
• Squares/Cubes
• Prime numbers
• Fibonacci series
• Alternating patterns

2. Alphabet Series

Involves alphabets with logical sequences based on:

• Position in the alphabet (A=1, B=2, …, Z=26)
• Forward or backward movement
• Skipping letters
• Reversals or pairings

3. Alphanumeric Series

A mixture of letters and numbers or symbols based on positions and patterns:

• e.g., A1, B2, C3…

4. Mixed Series

Involves a complex or alternating pattern:

• E.g., Numbers increase by 2 in one step, then decrease by 1.

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🧠 Strategies to Solve Series Completion:

🔹 Step 1: Observe the Pattern

Check if the series follows:

• A common mathematical operation
• Alphabetic positions
• Alternating or repeating logic

🔹 Step 2: Find the Difference

In number series, find the difference between consecutive terms.

🔹 Step 3: Check for Squared or Cubic Numbers

Many exams use squares or cubes in disguised patterns.

🔹 Step 4: Analyze Odd and Even Patterns

Alternating odd/even terms may indicate a hidden logic.

🔹 Step 5: Use Position Values for Alphabet Series

A = 1, B = 2, … Z = 26. Helps identify letter shifts.

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🔢 Examples & Explanation

✅ Example 1: Number Series

Q: 2, 6, 12, 20, ?, 42
Solution:
Differences:
6−2 = 4
12−6 = 6
20−12 = 8
⇒ Pattern: +2, +4, +6…
Next: 20 + 10 = 30, 30 + 12 = 42
Answer: ✅ 30

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✅ Example 2: Alphabet Series

Q: A, C, F, J, O, ?
Solution:
Positions: A(1), C(3), F(6), J(10), O(15)
Differences: +2, +3, +4, +5
Next: 15 + 6 = 21 → U
Answer: ✅ U

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✅ Example 3: Alphanumeric Series

Q: A1, C2, E3, G4, ?
Solution:
Letters: A, C, E, G → +2 in alphabet
Numbers: 1, 2, 3, 4 → +1
Next: I5
Answer: ✅ I5

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🧪 Practice Questions

Q1. 3, 9, 27, 81, ?

A) 162 B) 243 C) 324 D) 225
Answer: ✅ B) 243

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Q2. AZ, BY, CX, DW, ?

A) EV B) EU C) FU D) FX
Answer: ✅ B) EU

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Q3. 5, 10, 17, 26, ?

A) 35 B) 36 C) 37 D) 38
Answer: ✅ C) 37

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Q4. 1, 1, 2, 3, 5, 8, ?

A) 11 B) 12 C) 13 D) 14
Answer: ✅ C) 13 (Fibonacci series)

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Q5. 4, 16, 36, 64, ?

A) 100 B) 121 C) 81 D) 49
Answer: ✅ A) 100

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🎯 Quick Tips:

• Practice daily – speed comes with familiarity.
• Work on pattern recognition.
• Draw letter-number position tables for alphabet series.
• Skip tough ones in exams and come back later.