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.
Practice Question Papers
Practice Filters
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
- Arithmetic Series: Difference between consecutive terms is constant.
- Geometric Series: Each term is multiplied/divided by a constant factor.
- 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).
- Mixed Operator: Using multiple operations, e.g.,
(Term * 2) + 3. - Letter Clusters: Patterns applied to groups of letters (e.g., SCD, TEF, UGH...).
- Continuous Pattern Series: Small letters with blanks that form a repeating rhythmic pattern (e.g.,
abc_bc_ab_).
Typical Exam Weightage
| Exam | Typical 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
Q1. Complete the series: 3, 6, 11, 18, 27, ?
View Detailed Solution & ExplanationHide 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
Q3. Complete the series: SCD, TEF, UGH, ____, WKL
View Detailed Solution & ExplanationHide 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
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 & ExplanationHide 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