Series and coding questions reward systematic checking. Random guessing is slow; instead test position, difference, alternate terms, reverse order, prime/square/cube and alphabet shifts.
Core Definitions
Series
Standard definition: An ordered sequence whose next term follows a rule.
Exam meaning: Rule अनुसार अगाडि बढ्ने क्रम।
Coding-decoding
Standard definition: Representing information by a transformation rule and reversing or applying that rule.
Exam meaning: दिइएको rule बाट word/number परिवर्तन गर्ने र rule उल्ट्याउने काम।
How To Think
Think like a debugger. A series has a hidden algorithm. Coding has an encoding function. Your job is to infer the function from examples and apply it consistently.
Number Series Patterns
Start with simple differences, then move deeper.
- Constant difference: +3, +5, -2.
- Increasing difference: +2, +4, +8.
- Multiplication/division: x2, x3, /2.
- Squares/cubes: 1, 4, 9, 16 or 1, 8, 27.
- Prime/Fibonacci/alternate series.
- Mixed operation: x2+1, x3-2.
Coding Patterns
Most codes use position and transformation.
| Pattern | Example | Check |
|---|---|---|
| Alphabet shift | A->D | +3 position |
| Reverse alphabet | A->Z | 27 – position |
| Pair swap | ABCD->BADC | Swap adjacent |
| Vowel/consonant rule | Different shifts | Separate categories |
| Number substitution | CAT=3-1-20 | Alphabet positions |
Formulas and Rules
- Alphabet position: A=1, B=2, …, Z=26.
- Reverse alphabet pair: A-Z, B-Y, C-X; position sum = 27.
- nth odd number = 2n – 1; nth even number = 2n.
- Fibonacci-like series: next = previous two terms sum.
Step-by-Step Method
- For number series, calculate first differences.
- If differences fail, check second differences, multiplication and alternate terms.
- For letters, convert to positions.
- Check whether coding rule is uniform or category-based.
- Apply rule to all characters, then verify option fully.
Worked Examples
- 2, 6, 12, 20, 30: differences are 4,6,8,10, so next difference 12 gives 42.
- ACEG: positions 1,3,5,7, so next is I.
- If CODE is written as DPEF, each letter shifts +1. Then DATA becomes EBUB.
| Pattern | First Test | Second Test |
|---|---|---|
| Number series | Difference | Multiplication/alternate |
| Letter series | Position | Reverse/skip |
| Mixed series | Separate letters and numbers | Check relation between them |
| Coding | Shift/substitution | Vowel/consonant rule |
Exam Point
- Always write alphabet positions for letter questions.
- Check alternate term series before giving up.
- In coding, one example may not prove rule; test every letter.
- Avoid mental shortcuts when negative marking exists.
Visual Practice
- Keep A1-Z26 and reverse alphabet chart.
- Draw difference table under number series.
- Make two-row coding table: original and coded.
- Practice mixed letter-number grid.
Common Mistakes
- Testing only addition.
- Forgetting reverse alphabet.
- Ignoring alternate terms.
- Applying code to first letter only.
MCQ Revision
- What is A1-Z26?
- What is reverse pair of D?
- What is next after 2, 4, 8, 16?
- If CAT=DBU, what is DOG?
- When should alternate series be checked?
Final Summary
- Series questions are hidden algorithms.
- Difference table is the fastest start.
- Coding needs exact transformation.
- Alphabet position mastery saves time.