How to Solve Coding – Decoding? Concept & Tips

By BYJU'S Exam Prep

Updated on: September 25th, 2023

Dear Aspirants,

We are here providing you some Important Concepts & Short Tricks on Coding – Decoding Questions in Reasoning which are usually asked in Bank Exams. Use these below-given shortcuts to solve questions within minimum time. These shortcuts & Concept will be very helpful for your upcoming All Bank Exam 2023.

To make the chapter easy for you all, we are providing you all some Important Concept & Short Tricks on Coding – Decoding?  which will surely make the chapter easy for you all.

About the Coding and Decoding:-

Coding is a method of transmitting a message between the sender and the receiver without a third person knowing it. Before transmitting, the data is encoded and at receiver’s side, the data is decoded in order to obtain original data by determining common keys in encoded data.

Coding and Decoding forms a dedicated part of the Reasoning Section in various competitive exams but the level of questions differs in them. For example in SSC, the level of questions in easy to medium while in IBPS exams, the level of questions is difficult. In IBPS, coding and decoding questions comes under Machine Coding and Decoding Topic.

What is the approach to solve the questions of this section?

  • Observe alphabets or numbers given in the code keenly.
  • Find the sequence it follows whether it is ascending or descending.
  • Detect the rule in which the alphabets/numbers/words follow.
  • Fill the appropriate letter/number/word in the blank given.

Some Basics which we need to learn before solving the questions of this topic are:

  • Letter position (A=1, B=2, C=3, D=4 …… Y=25, Z=26)
  • Opposite position of letters (A=26, B=25 …… Z=1)
  • Opposite of each letter (A is opposite to Z and B is opposite to Y and C is opposite to X …… and so on)

Various types on which Coding and Decoding are classified are (as per Bank Exams):

  • Letter Coding
  • Substitution
  • Mixed Letter Coding
  • Mixed Number Coding

Let us analyse them in detail


In this type, the real alphabets in a word are replaced by certain other alphabets according to a specific rule to form its code. The candidate is required to detect the common rule and answer the questions accordingly.

For Example:

In a certain code, “CODING” is written as “DPEJOH”. How will DECODING be written in that code?


Compare 1st letter of CODING with 1st letter of DPEJOH.

C is converted to D.

You know C’s next letter in alphabets is D.

O’s next letter is P.

D’s next letter is E.

I’s next letter is J.

N’s next letter is O.

G’s next letter is H.

This was how CODING was converted to DPEJOH. Now in the same way you have to convert DECODING.

So D is converted to E.

E-F, C-D, O-P, D-E, I-J, N-O, G-H

So DECODING should be converted to EFDPEJOH.


In this section, object names are substituted with different object names. We should carefully trace the substitution and answer the given question.

For Example:

If white is called blue, blue is called red, red is called yellow, yellow is called green, green is called black, black is called violet and violet is called orange, what would be the colour of human blood?

1. Red

2. Green

3. Yellow

4. Violet

5. Orange

Ans: C


The colour of the human blood is ‘red’, and as it is given that ‘red’ is called ‘yellow’. So, the colour of human blood is ‘yellow’.


In Mixed letter coding type of questions, three or four complete messages are given in the coded language and the code for a particular word is asked. To analyze such codes, any two messages bearing a common word are picked up. The common code word will mean that word. Proceeding similarly by picking up all possible combinations of two, the entire message can be analyzed.

For Example:

In a certain code language,

1. ‘pod na joc’ means ‘very bright boy’;

2. ‘tam nu pod’ means ‘the boy comes’;

3. ‘nu per ton’ means ‘keep the doll’;

4. ‘joc ton su’ means ‘very good doll’.

Which of the following means ‘bright’ in the same code language?

1. joc   2. pod   3. ton   4. na    5.None of these

Ans: D


In statements (a) and (b), the common code word is ‘pod’ and the common word is ‘boy’.

So, ‘pod’ stands for ‘boy’.

In statements (a) and (d), the common code word is ‘joc’ and the common word is ‘very’.

So, ‘joc’ stands for ‘very’.

So, in (a) ‘na’ stands for ‘bright’.


In this type of questions, a few groups of numbers each coding a certain short message, are given. Through a comparison of the given coded messages, taking two at a time, the candidate is required to find the number code for each word and then formulate the code for the message given.

For Example:

In a certain code,

‘786’ means ‘study very hard’,

‘958’ means ‘hard work pays’

‘645’ means ‘study and work’.

Which of the following is the code for ‘very’?

1. 7   2. 5   3. 8  4.6  5. Either 6 or 7

Ans: 1


In the first and second statements, the common word is ‘hard’ and the common code digit is ’8’. So, ‘8’ means ‘hard’.

In the first and third statements, the common word is ‘study’ and the common code digit is ‘6’. So, ’6’ means ‘study’.

Thus, in the first statement ‘7’ means ‘very’.

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