Reasoning

Number & Letter Series Guide & Practice

Master arithmetic, geometric, alternating, Fibonacci, and letter series pattern recognition with explanations, shortcuts and mock sets. Explore dynamic solver blueprints, master fundamental equations, examine step-by-step solved examples, and practice with real exam-grade mock test sets.

Featured in:SSC CGLSSC CHSLIBPS POIBPS ClerkRRB NTPCRRB Group D

Practice Question Papers

Practice Filters

Reasoning

Series - Set 4 Practice Test

Jun 2026No attempts yet
25 Qs
37 min
Easy
Reasoning

Series - Set 3 Practice Test

Jun 2026No attempts yet
25 Qs
37 min
Easy
Reasoning

Series - Set 2 Practice Test

Jun 2026No attempts yet
25 Qs
37 min
Easy
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Video Tutorial

Number & Letter Series Short Tricks & Formulas

Watch this short trick video explaining high-speed shortcuts, mental math formulas, and patterns for Number & Letter Series. Master the theory and start practicing with the tests below.

Foundation & Concepts

1. Letter Series Foundation

  • Alphabetical Positions: Standard (A=1...Z=26).
  • EJOTY Concept: E=5, J=10, O=15, T=20, Y=25. Helps locate any letter quickly.
  • RHS Counting: To find the position of a letter from the Right Hand Side (Z to A), use: 27 - (Position from Left).
    • Example: The 10th letter from the left (J) is the (27-10) = 17th letter from the right.
  • Central Letter: To find the middle letter between two positions from the same side, take the average of their positions.
    • Example: Middle of 12th (L) and 20th (T) is (12+20)/2 = 16th (P).

2. Number Series Foundation

  • Sequence: A set of numbers following a specific mathematical rule.
  • Common Logic:
    • Addition/Subtraction (Constant or increasing/decreasing difference).
    • Multiplication/Division.
    • Squares and Cubes (n², n³, n²+1, etc.).
    • Fibonacci (Sum of previous two terms).

Patterns/Rules

  1. Arithmetic Series: Difference between consecutive terms is constant.
  2. Geometric Series: Each term is multiplied/divided by a constant factor.
  3. Alternating Series: Two or more different patterns running in parallel (e.g., terms 1, 3, 5 follow one rule; terms 2, 4, 6 follow another).
  4. Mixed Operator: Using multiple operations, e.g., (Term * 2) + 3.
  5. Letter Clusters: Patterns applied to groups of letters (e.g., SCD, TEF, UGH...).
  6. Continuous Pattern Series: Small letters with blanks that form a repeating rhythmic pattern (e.g., abc_bc_ab_).

Typical Exam Weightage

ExamTypical Questions
SSC (CGL / CHSL / MTS)2–3 questions
Banking (IBPS / SBI)5 questions (usually a full standalone set)
Railways (RRB)2–3 questions

In Banking Prelims this is typically a dedicated 5-question set — pattern-recognition speed matters more than any formula.

Figures are typical ranges based on recent-year patterns, not a guarantee for any specific upcoming paper — always cross-check against the latest official syllabus and previous-year papers for Number & Letter Series.

Solved Examples

1Solved Example
Easy

Q1. Complete the series: 3, 6, 11, 18, 27, ?

View Detailed Solution & Explanation
Step-by-Step Explanation

The differences are increasing odd numbers:

  • 3 + 3 = 6
  • 6 + 5 = 11
  • 11 + 7 = 18
  • 18 + 9 = 27
  • 27 + 11 = 38
  • Answer: 38

Q2. Complete the series: B, F, J, N, ?

  • Solution: Positional values: B(2), F(6), J(10), N(14). Constant increase of +4.
    • 14 + 4 = 18 (R).
  • Answer: R
2Solved Example
Moderate

Q3. Complete the series: SCD, TEF, UGH, ____, WKL

View Detailed Solution & Explanation
Step-by-Step Explanation
  • First letter: S, T, U, V, W (+1 shift).
    • Second/Third letters: CD, EF, GH, IJ, KL (Alphabetical pairs).
  • Answer: VIJ

Q4. Find the missing term: 12, 13, 25, 38, ?, 101

  • Solution: Fibonacci pattern (sum of previous two):
    • 12 + 13 = 25
    • 13 + 25 = 38
    • 25 + 38 = 63
    • 38 + 63 = 101
  • Answer: 63

Q5. ZA5, Y4B, XC6, W3D, _____

  • Solution:
    • 1st letter: Z, Y, X, W, V (Reverse alphabetical).
    • 2nd letter: A, B, C, D, E (Forward alphabetical).
    • Number: 5, 4, 6, 3, 7 (Alternating -1, +2, -3, +4).
  • Answer: VE7
3Solved Example
Hard

Q6. Which set of letters completes the pattern? ab_accab_acc_bba_cabba_c

  • Options: (a) bcabb, (b) acbcc, (c) bbacc, (d) bcbba
View Detailed Solution & Explanation
Step-by-Step Explanation

Divide the series into segments to find a repeating pattern. The pattern is abb/acc/abb/acc/abb/acc.

  • Filling the blanks: b, b, a, c, c.
  • Answer: bbacc

Q7. In a certain code, COMPUTER is written as RFUVQNPC. How will MEDICINE be written?

  • Solution: Reverse the word and shift internal letters +1. (See Coding-Decoding for detail).
  • Answer: EOJDJEFM

Q8. Find the missing term: 5, 7, 21, 55, ?, 215

  • Solution: Mixed operator logic:
    • 5 + (2² - 2) = 5 + 2 = 7
    • 7 + (4² - 2) = 7 + 14 = 21
    • 21 + (6² - 2) = 21 + 34 = 55
    • 55 + (8² - 2) = 55 + 62 = 117
    • 117 + (10² - 2) = 117 + 98 = 215
  • Answer: 117