Coding Decoding - Notes | UPSC Prelims Paper 2 CSAT - Quant, Verbal & Decision Making PDF Download

Coding - Decoding

Coding is a system of signals. This is a method of transmitting information in the form of codes or signals without it being known by a third person.

The person who transmits the code or signal is called the sender and the person who receives it, is called the receiver. Transmitted codes or signals are decoded on the other side by the receiver—this is known as decoding.

Most competitive exams have a dedicated section of Coding –Decoding in Reasoning or Mental Ability. Many of students and readers find difficulty to solve questions based on Coding – Decoding in Mental Aptitude.

The Coding and Decoding Test is set up to judge the candidate’s ability.

How To Solve Coding Decoding Questions

a) Observe alphabets or numbers given in the code keenly.

b) Find the sequence it follows whether it is ascending or descending.

c) Detect the rule in which the alphabets/numbers/words follow.

d) Fill the appropriate letter/number/word in the blank given.

In questions on codes, a word (basic word) is coded in a particular way and the candidates are asked to code other words in the same way. The coding and decoding tests are set up to judge the candidate’s ability to decipher the rule that has been followed to code a particular word/message and break the code to decipher the message.

The Coding and Decoding is classified into Six types according to the on what way it is doing. They are 

1. Letter Coding
2. Number Coding
3. Mixed Coding
4. Mixed Number Coding
5. Decoding
6. Symbols Coding

1. Letter Coding - 

A particular letter stands for another letter in letter coding.
Eg: If COURSE is coded as FRXUVH, how is RACE coded in that code?

(1) HFDU 

(2) UCFH 

(3) UDFH

(4) UDHF 

(5) UDFG

In the given code, each letter is moved three steps forward tan the corresponding letter in the word. So R is coded as U, A as D, C as F, E as H. Hence (3) is the answer.

Learn this table by heart. This is the only shortcut or trick to solve coding - decoding questions fast in Bank exams.

2. Number Coding - 

In these questions, either numerical code values are assigned to a word or alphabetical code values are assigned to numbers. The candidate is required to analyze the code as per directions.

Case I: When numerical values are assigned to words.

Eg: If in a certain code ROPE is coded as 6821, CHAIR is coded as 73456 what will be the code forCRAPE?

(1) 73456 

(2) 76421 

(3) 77246

(4) 77123 

(5) None of these

Clearly, in the given code, the alphabets are coded as follows.

        R   O   P   E   C   H   A   I

        6    8   2    1   7    3    4    5

So CRAPE is coded as 76421, So the answer is (2)

Case II: When alphabetical code values are assigned to the numbers.

Eg: In a certain code 3456 is coded as ROPE & 15546 is coded as APPLE. Then how is 54613 coded?

(1) RPPEO 

(2) ROPEA 

(3) POEAR

(4) PAREO 

(5) None of these

Clearly in the given figures, the numbers are coded as follows.

      3    4    5     6     1     4

      R   O    P    E     A    L

So 54613 is coded as POEAR. The answer is (3)

3. Mixed Coding  - 

In this type of question, three or four complete messages are given in the coded language and the code for a particular word is asked. 

To analyse such codes, any two messages bearing the common word are picked up. 

The common code word will mean that word. Proceeding similarly by picking up all possible combinations of two messages the entire message can be analyzed.

Eg: If tee see pee means drink fruit juice, see kee lee means juice is sweet, and lee ree mee means he is  intelligent, which word in that language means sweet?

(1) see 

(2) kee 

(3) lee

(4) pee 

(5) tee

In the first and the second statements the common word is juice and the common code word is see. So seemeans juice. In the second and the third statements, the common word is ‘is’ and the common code is lee. So lee means is. Thus in the second statement, the remaining word sweet is coded as kee. Hence the answer is (2)

4. Mixed Number Coding - 

In this type of questions, three or four complete messages are given in the coded language and the code number for a particular word is asked.

Eg: If in a certain code language, 851 means good sweet fruit; 783 means good red rose and 341 meansrose and fruit which of the following digits stands for sweet in that language?

(1) 8 

(2) 5 

(3) 1

(4) 3 

(5) None of these

In the first and the second statements, the common code digit is 8 and the common word is good. So8 stands for good. In the first and the third statements, the common code digit is 1 and the common word is fruit. So 1 stands for fruit. Therefore in the first statement, 5 stands for sweet. Hence the answer is (2).

In these questions, artificial or code values are assigned to a word or a group of words and the candidate is required to find out the original words.

Eg: If in a certain language FLOWER is written as EKNVDQ, what will be written as GNTRD?

(1) HEOUS 

(2) HOUES 

(3) HUOSE

(4) HOUSE 

(5) None of these

Each letter of the word is one step ahead of the corresponding letter of the code.

E K N V D Q                  G N T R D

F  L O W E R                  H O U S E

Thus HOUSE is written as GNTRD, So the answer is (4)

This is a kind of coding recently included in the Reasoning section. In this type of questions either alphabetical code values are assigned to symbols or symbols are assigned to alphabets. The candidate is required to analyse the code as per direction.

Eg: 1. In a certain code ‘TOME’ is written as ' @ $ * ? ' and ARE is written as ‘ • £ ? ’ How can ‘REMOTE’ be written in that code?

(1) £ ? • $ @ ? 

(2) @ ? * $ @ ? 

(3) £ ? * $ @ ?

(4) Cannot be determined 

(5) None of these

Sol: From the data we have

T - @ 

O - $ 

M - * 

E - ? 

A - • 

R - £ 

E - ?

Hence REMOTE is coded as £ ? * $ @ ? So (3) is the answer.