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Coding can be described as a system of signals and it is simply a technique of transmitting information in the form of codes or signals without a third person knowing about it. The person, who is responsible for transmitting the code or signal, is known as the sender and the receiver is the person who receives it. All the codes or signals that are transmitted get later decoded on the other side by the receiver—which is called decoding. In this article, find all you need to know about coding and decoding.

The most competitive exams come with a special section of Coding & Decoding in Reasoning or Mental Ability. A lot of students and readers find it difficult to solve questions on Coding and Decoding in Mental Aptitude.

Logical Reasoning

What is Logical Reasoning?

Simply put, there are two kinds of logical reasoning that can be distinguished in addition to apart from formal deduction: induction and abduction. Let’s assume that there’s a precondition or premise, a conclusion or logical consequence and a rule or material conditional given that signifies the conclusion given the precondition. So, we can explain that:

  • Deductive reasoning is all about finding out whether the truth of a conclusion can be determined for that rule, which is based completely on the truth of the premises. For instance: “Things outside get wet when it rains. The grass is outdoors, so naturally, when it rains, the grass becomes wet.” All types of mathematical logic and philosophical logic are normally connected to this style of reasoning.
  • Inductive reasoning makes attempts to hold up a determination of the rule. It hypothesizes a rule after taking into consideration a lot of examples that follow from a precondition in terms of such a rule. Case in point: “The grass became wet many times when it started raining, so whenever it rains, the grass always gets wet.” While these may be persuasive, this point of view is not deductively valid and science is associated with this type of reasoning.
  • Abductive reasoning, also known as inference, picks up a cogent set of preconditions. Given a true conclusion and a rule, it is all about selecting some probable premises that, if true also, can aid the conclusion, though not exclusively. Example: “The grass gets wet when it rains. The grass is located outside, so naturally, nothing is dry outside. Therefore, it must have rained, maybe.” Diagnosticians and detectives commonly use this type of reasoning.

How to Solve Coding and Decoding Questions

  1. a) Study the numbers or alphabets given in the code properly.
  2. b) Figure out whether it follows the ascending or descending sequence.
  3. c) Identify the rule wherein the alphabets/numbers/words follow.
  4. d) Now, fill in the appropriate number/ letter/word in the blank space given.

When it comes to questions about coding and decoding, a word (basic word) is coded in a certain way and the candidates get asked to code other words in the same way. All the coding and decoding tests get set up for judging a candidate’s capacity to decode the rule that has been followed to code a particular word/message and then break the code to interpret the message.

There are 6 types of Coding and Decoding:

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

1. Letter Coding

In this case, a certain letter stands for another letter in letter coding.

E.g.: If COURSE has been coded as FRXUVH, how can we code RACE in that code?

(1) HFDU

(2) UCFH

(3) UDFH

(4) UDHF

(5) UDFG

In this code given above, every letter is moved three steps forward than the corresponding letter in the word. Therefore, R gets coded as U, A as D, C as F, E as H. For this reason, (3) is the answer.

You need to learn the following table by heart. It is the only trick to solve coding and decoding questions quickly in your bank exams.

Alphabets Alphabetical Order Reserve Order
A 1 26
B 2 25
C 3 24
D 4 23
E 5 22
F 6 21
G 7 20
H 8 19
I 9 18
J 10 17
K 11 16
L 12 15
M 13 14
N 14 13
O 15 12
P 16 11
Q 17 10
R 18 9
S 19 8
T 20 7
U 21 6
V 22 5
W 23 4
X 24 3
Y 25 2
Z 26 1

2. Number Coding 

When it comes to these questions, either alphabetical code values are assigned to numbers or numerical code values are assigned to a word. Candidates need to analyse the code as per directions.

Case I: When numerical values are assigned to words.

E.g.: Talking about a certain code, ROPE is coded as 6821 and CHAIR is coded as 73456. So, how would you code for CRAPE?

(1) 73456

(2) 76421

(3) 77246

(4) 77123

(5) None of these

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


6 8 2 1 7 3 4 5

So, CRAPE would be coded as 76421 and the answer is (2).

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

E.g.: In a particular code3456 is coded as ROPE 15546 is coded as APPLE. Then, how would you code 54613?





(5) None of these

As per the given figures, the numbers can be coded as follows.

3 4 5 6 1 4


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

3. Mixed Coding

In this type, there are 3 or 4 complete messages given in the coded language and the code for a particular word is asked.

For working out such coding and decoding problems, any two messages having a common word are picked up. The common code word will mean that word. Similarly, we would pick up all possible combinations and with the help of two messages, the entire message can be figured out.

E.g.: If tee see pee implies drink fruit juicesee kee lee denotes juice is sweet, and lee ree mee simply means she is intelligent, then as pre these clues, which word in that language would mean sweet?

(1) see

(2) kee

(3) lee

(4) pee

(5) tee

Note that in the 1st and the 2nd statements, the common word is juice and the common codeword is see. Therefore, see means juice. Coming to the 2nd and 3rd statements, the common word is ‘is’ and the common code is lee. So, naturally, lee implies is. Therefore, in the second statement, the remaining word sweet is coded as kee. Thus, the answer is (2).

4. Mixed Number Coding

Here, 3 or 4 complete messages are given in the coded language and the code number for a particular word is asked.

E.g.: When it comes to a particular code language, 851 denotes good sweet fruit783 denotes good red rose and 341 means rose and fruit. So, in this situation, which of the following digits stands for sweet in that language?

(1) 8

(2) 5

(3) 1

(4) 3

(5) None of these

Talking about the 1st and the 2nd statements, the common code digit is and the common word is good. As a result, means good. In the 1st and the 3rd statements, the common code digit is and the common word is fruit. Thus, denotes fruit. So, in the 1st statement, stands for sweet. Now, the answer is (2).

5. Decoding 

In decoding questions, artificial or code values are given to a word or a group of words and the students need to find out the original words.

E.g.: If in a particular language, FLOWER gets written as EKNVDQ, what would GNTRD stand for?





(5) None of these

Note that every letter of the word is one step ahead of the corresponding letter of the code.



Therefore, HOUSE would be written as GNTRD and the answer is (4).

6. Symbols Coding 

This type of coding has been included recently in the Reasoning section. Here, either of the symbols is assigned to alphabets or alphabetical code values are assigned to symbols. The candidate needs to analyse the code as per direction.

E.g.: 1. Let’s say that ‘TOME’ is written as ‘ @ $ * ? ’and ARE is written as ‘ • £ ? 

So, how would we write ‘REMOTE’ in that code?

(1) £ ? • $ @ ?

(2) @ ? * $ @ ?

(3) £ ? * $ @ ?

(4) Cannot be determined

(5) None of these

Ans: From the data we have:

T – @

O – $

M – *

E – ?

A – •

R – £

E – ?

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

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