Thinking & Decision Making

Module 1

1. Number & Letter Series

Pattern recognition in number and letter sequences

Theory

Number & Letter Series

Pattern Recognition - Find the hidden rule in sequences

What You'll Learn

  1. Identify patterns in number series
  2. Solve letter series problems
  3. Handle mixed (alphanumeric) series
  4. Apply quick tricks for exams

1. Number Series Patterns

Addition/Subtraction Series

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Pattern: Add or subtract a constant

Example 1: 2, 5, 8, 11, ?
Difference: +3, +3, +3, +3
Answer: 14

Example 2: 100, 90, 80, 70, ?
Difference: -10, -10, -10, -10
Answer: 60

Multiplication/Division Series

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Pattern: Multiply or divide by a constant

Example: 3, 6, 12, 24, ?
Ratio: ×2, ×2, ×2, ×2
Answer: 48

Example: 256, 64, 16, 4, ?
Ratio: ÷4, ÷4, ÷4, ÷4
Answer: 1

Square/Cube Series

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Pattern: Perfect squares or cubes

Squares: 1, 4, 9, 16, 25, ? = 36 (1², 2², 3², 4², 5², 6²)
Cubes: 1, 8, 27, 64, ? = 125 (1³, 2³, 3³, 4³, 5³)

Alternate/Mixed Series

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Two patterns alternating

Example: 2, 5, 3, 6, 4, ?
Pattern 1: 2, 3, 4 (position 1, 3, 5: +1)
Pattern 2: 5, 6, ? (position 2, 4, 6: +1)
Answer: 7

Fibonacci-like Series

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Each term = sum of previous two terms

Example: 1, 1, 2, 3, 5, 8, ?
1+1=2, 1+2=3, 2+3=5, 3+5=8, 5+8=13
Answer: 13

2. Letter Series

Position Values

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A=1, B=2, C=3, ... Z=26

Trick: L=12 (middle), M=13
Quick: A=1, E=5, I=9, O=15

Skip Pattern

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Example: A, C, E, G, ?
Skip: +2 letters each time
Answer: I

Example: Z, X, V, T, ?
Skip: -2 letters each time
Answer: R

Opposite Letters

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A↔Z (1+26=27), B↔Y, C↔X, D↔W...
Sum of positions = 27

Example: If A→Z, then M→?
M=13, so opposite = 27-13 = 14 = N

3. Mixed Series

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Example: A1, B2, C3, D4, ?
Pattern: Letter advances +1, Number advances +1
Answer: E5

Example: Z1, Y2, X3, W4, ?
Pattern: Letter goes backward, Number goes forward
Answer: V5

Key Tricks

Pattern TypeHow to Identify
ArithmeticConstant difference
GeometricConstant ratio
Squares1, 4, 9, 16... check if n²
FibonacciSum of previous two
AlternateCheck odd/even positions separately

Quick Solving Steps

  1. Find differences between consecutive terms
  2. If differences are constant → arithmetic
  3. If differences increase/decrease → check ratios or squares
  4. If no pattern → check alternate positions
Practice

Test your understanding

📝

Practice Quiz

10 questions · 90s per question

Each question has a 90-second time limit. Unanswered questions will be auto-submitted when time runs out.