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.