Reasoning Chapters

1. NUMBER AND LETTER SERIES2. ALPHANUMERIC SERIES3. MISSING NUMBER4. ANALOGY SIMILARTY5. CLASSIFICATION6. DIRECTION 7. BLOOD RELATION8. SEATING ARRANGEMENT9. PUZZLE10. ORDER AND RANKING11. SYLLOGISM12. CLOCK13. CALENDER14. WORD FORMATION15. DICE16. CUBE AND CUBOID17. MIRROR AND WATER IMAGE18. VENN DIAGRAM19. STATEMENT AND ASSUMPTION

Number & Letter Series

Number and letter series are common topics in reasoning sections of competitive exams, involving patterns based on logic, arithmetic operations, and positions of letters.

Concept of Number Series

A number series is a sequence of numbers arranged in a particular pattern. The task is to find the missing number or identify the next number in the series.

Types of Number Series:

  • Arithmetic Series (constant addition/subtraction)
  • Geometric Series (multiplication/division)
  • Square/Cube Series
  • Mixed Operations
  • Alternating Series

Example:

Q: 2, 4, 8, 16, ?
Ans: 32 (Each term is multiplied by 2)

Concept of Letter Series

A letter series is a sequence of alphabets following a particular pattern. You need to find the missing letter or the next letter in the sequence.

Types of Letter Series:

  • Forward Alphabetical Series
  • Backward Alphabetical Series
  • Skipping Letters
  • Position-based Series (A=1, B=2, etc.)

Example:

Q: A, C, E, G, ?
Ans: I (Each letter is 2 steps ahead)

30+ Previous Year Questions with Solutions

  1. SSC CHSL 2020: 7, 14, 28, 56, ?
    Answer: 112 (Each number is multiplied by 2)
  2. RRB NTPC 2019: 121, 144, 169, 196, ?
    Answer: 225 (Squares of 11,12,13,14,...)
  3. SSC CGL 2018: A, D, G, J, ?
    Answer: M (+3 each time)
  4. HSSC Group D 2018: 3, 6, 18, 72, ?
    Answer: 360 (×2, ×3, ×4, ×5)
  5. SSC GD 2021: 2, 3, 5, 8, 12, ?
    Answer: 17 (+1, +2, +3, +4, ...)
  6. SSC MTS 2019: AZ, BY, CX, ?
    Answer: DW (A-Z, B-Y, C-X, D-W)
  7. RRB JE 2015: 1, 4, 9, 16, ?
    Answer: 25 (1², 2², 3², 4², 5²)
  8. SSC CPO 2017: K, J, H, E, ?
    Answer: A (-1, -2, -3, -4)
  9. HSSC JE 2017: 4, 5, 9, 14, 23, ?
    Answer: 37 (+1, +4, +5, +9, +14)
  10. SSC CHSL 2016: B, E, H, K, ?
    Answer: N (+3)
  11. SSC Stenographer 2020: 90, 80, 70, ?, 50
    Answer: 60 (Decreasing by 10)
  12. RRB Group D 2018: 1, 1, 2, 3, 5, 8, ?
    Answer: 13 (Fibonacci series)
  13. SSC MTS 2017: Z, X, V, T, ?
    Answer: R (-2)
  14. SSC CGL 2021: 3, 9, 27, 81, ?
    Answer: 243 (×3)
  15. HSSC Clerk 2016: 10, 20, 30, 50, 80, ?
    Answer: 130 (+10, +10, +20, +30, +50)
  16. SSC CGL 2015: C, F, I, L, ?
    Answer: O (+3)
  17. SSC GD 2019: 729, 243, 81, 27, ?
    Answer: 9 (÷3)
  18. RRB ALP 2014: 2, 3, 5, 7, 11, ?
    Answer: 13 (Prime numbers)
  19. SSC JE 2020: 81, 64, 49, 36, ?
    Answer: 25 (Squares of 9,8,7,6,...)
  20. SSC CHSL 2019: D, G, J, M, ?
    Answer: P (+3)

Tips to Solve Series Questions

  • Always check for common patterns like +, –, ×, ÷, squares, cubes.
  • For letter series, use position values (A=1, B=2, ... Z=26).
  • Identify alternating or dual sequences.
  • Write down differences between terms to identify patterns.
  • Practice different types regularly to improve speed and accuracy.
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