• CODING-DECODING is an important part of Logical reasoning section in all aptitude related examinations. 
  • Coding is a process used to encrypt a word, a number in a particular code or pattern based on some set of rules. 
  • Decoding is a process to decrypt the pattern into its original form from the given codes. 
  • Letter Coding In this type of questions, alphabets of a word are replaced by some other alphabets according to specific rule to form code. 
  • Number Coding In this type of questions, a word is replaced by certain numbers according to some specific rule. 
Types of Coding and Decoding

  1. Letter Coding
  2. Number/Symbol coding
  3. Substitution coding

(1). Letter Coding :-
  • Letter coding-decoding in which the letter of words is replaced by certain other letters according to specific patterns/rules to form a code.
  • Example for Letter coding-decoding. Detect the coding pattern /rule and answer the question below.
  • If BROWN is written as ‘ZPMUL’, then VIOLET is coded as....
  1.  TGMJCR
  4. TGWCQ
Answer : In this question, the alphabet is replaced with another alphabet with some directions. The first letter B is coded as Z means that it moves backward with 1 letter similarly R is coded as P, O is coded as M,W is coded as U, and N is coded as L. So VIOLET is coded as TGMJCR.
  • VIOLET is coded as TGMJCR

(2). Number/Symbol coding :-
  • Number coding-decoding in which either the numerical code values are assigned to a word or alphabetical code letters are assigned to the numbers.
  • Example for Number/Symbol coding-decoding.
  • If CHAIR is written as ‘12345’, RENT is written as ‘5678’, and then REAR is written as.
  1. 5635
  2. 5356
  3. 5365
  4. 5653
Answer : In this question each alphabet is coded as a number. So that CHAIR is coded as 12345 and RENT is coded as 5678 and the REAR is coded as 5635.
  • REAR is coded as 5635.

(3). Substitution coding :-
  • Substitution coding-decoding in which some particular words are assigned with certain substituted names.
  • Example for Substitution coding-decoding.
  • If a dog is called “cat”, cat is called “lion”, lion is called “rat”, then which of these lives in a forest?
  1. Rat
  2. Lion
  3. Dog
  4. Cat
Answer : In this question, lion lives in the forest but lion is called a rat so rat lives in a forest is the answer.