Coding & Decoding | Logical Reasoning (LR) and Data Interpretation (DI) - CAT PDF Download

What is ‘Coding-Decoding’?

• Coding is a way of transmitting data between the sender and the receiver in an encrypted manner i.e. without any other person knowing about it.
• Before transmission, the data is encoded and when it is received, it is decoded in order to obtain the original data.
• This prevents the data from getting corrupt and leaked.

Types of Coding Decoding Questions

Let us see the various types of reasoning questions on coding decoding one by one below: Types of Coding Decoding 

1. Letter coding

In this type of questions, the alphabets in a word are replaced by other alphabets according to a specific rule.

To solve the coding decoding reasoning questions, first of all it is necessary to remember the positions of all alphabetical letters, both in forward and backward order, which is given below.
Positional Value of Alphabets in forward direction

Positional Value of Alphabets in backward direction

Q. In a certain code, “PARKING” is written as “RYTIKLI”. How will FLOWERS be written in that code?
Explanation: Find out the pattern by comparing the 1st letter of PARKING with the 1st letter of RYTIKLI.
We observe that P is converted to R. R is two positions after P.
Now A is converted to Y. So, we can conclude that A is two positions before Y.
So, PARKING is coded as +2 and -2 alphabets in an alternate manner.
Using the same logic, we can decode flowers
F – (+2) – H
L – (-2) – J, as so on
The correct answer is ‘HJQUHPQ’.

2. Substitution

In such questions, names/words are substituted with different names/words. We have to carefully trace the substitution to arrive at the correct answer.
For instance: If ‘Parrot’ is known as ‘Peacock’, ‘Peacock’ is known as ‘Swallow’, ‘Swallow’ is known as ‘Pigeon’, ‘Pigeon’ is known as ‘Sparrow’, what would be the name of the national bird?
Explanation: We know ‘peacock’ is the national bird. But in the given question, ‘Peacock’ is coded as ‘Swallow’. So ‘Swallow’ is the correct answer.

3. Mixed Letter Coding

In this type of question, three-four phrases are given in coded language and the code for a particular word is asked.
To solve such questions, any two phrases with a common word are picked up. The common code word will refer to that word. Proceeding in a similar manner, all possible combinations of two phrases are selected and a common code is picked up.
Q. In a certain code language,

• ‘new banking system’ means ‘ss tp na’
• ‘officer in uniform’ means ‘or mu at’
• ‘new bank officer’ means ‘or bk na’
• ‘systems in bank’ means ‘bk at ss’

What is the code for ‘in’?
Ans: In statements (2) and (4), the common code word is ‘in’ and the common code is ‘at’.

What does the code ‘bk’ stand for?
Ans: In statements (3) and (4), the common code word is ‘bk’ and the common word for that is ‘bank’.

4. Mixed Number Coding

In this type of questions, numbers are given corresponding to phrases. Following the same rule as in the above case, we can easily find out the answer. Selecting two phrases at a time, you have to find out the number code for each word and then arrive at the correct answer.

Q. In a certain code,
‘467’ means ‘leaves are green’,
‘485’ means ‘green is good’
‘639’ means ‘they are paying’.

What is the number code for ‘leaves’?
Ans: In statements 1 and 3, the common word is ‘green’ and the common number is ‘4’. So, ‘4’ is for ‘green’. Now, in statements 1 and 2, ‘are’ is common and ‘6’is common. So, ‘6’ stands for ‘are’.
In statement 1, only ‘leaves’ and ‘7’ are remaining, therefore ‘leaves’ corresponds to ‘7’.

5. Letter to Number Coding 

In this type of coding decoding reasoning, either numerical code values are assigned to a word or alphabetical code letters are assigned to the number. 

6. Substitutional Coding 

In these type of coding decoding questions, words are encrypted or coded with the suitable word. 

7. Chinese Coding

In these type of coding and decoding reasoning questions, a few statements consisting of the same words but in different order will be coded as words or symbols or letters. Candidates need  to find the codes of words by finding the common words in different statements as the code of a word in both the statements will be the same. 

8. LSN Coding 

In this type of coding decoding reasoning, words of different statements are coded with letters, symbols and numbers by using different operations. Candidates need to find the logic used for letter, symbol, and number. 

9. Conditional Coding

In this type of coding decoding reasoning, a few operations will be given and candidates need to apply all the given conditions to find the code of a given word. 

10. Binary Coding 

In these type of coding decoding reasoning questions, decimal numbers are coded by binary numbers such as 0 and 1. 

Tips and Tricks to Solve Coding Decoding Questions

Candidates can find various tips and coding decoding reasoning tricks from below for solving the questions related to this section.
Tip # 1: EJOTY will help the candidates to find nearby letters quickly. The same is given below.

Tip # 2: To solve the Letter-to-Letter coding decoding questions quickly, candidates need to check if the opposite letters are given in the code. Then candidates need to check if the position of letters is interchanged. Finally check if operations like addition or subtraction is applied. 

Tip # 3: To solve the letter to number type coding and decoding reasoning questions quickly, candidates first need to check if the positional values of letters are given in the code. Then check if the position of positional values of letters are interchanged. Check if the positional values of letters are reversed alphabetical series. Check if the position of positional values of letters are interchanged. Finally check if operations like addition, subtraction or multiplication is applied. 

Smart Approach to Solve ‘Coding-Decoding’ Questions

• Observe alphabets or numbers given in the question
• Try to find the pattern or sequence it follows. 
• They could be in ascending or descending order, arranged in an alternate fashion and other ways as well.
• Figure out the rule followed by the given arrangement of alphabets/numbers/words

Basic points you need to remember before solving any question of this topic.

• Alphabets’ positions (A=1, B=2,……,Y=25, Z=26)
• Opposite position of alphabet (A=26, B=25,……, Z=1)
• Opposite of each alphabet (A is opposite to Z, B is opposite to Y and so on)

Sample Coding Decoding Questions 

Example1: In the following questions find out the alternatives which will replace the question mark. 

ENGLISH : FOHNHRG :: SCIENCE : ?
Sol: Here ENGLISH is written as follows.
If we follow the same principle for SCIENCE then we get the word TDJGMBD. Hence, it is the correct answer.

Example 2: In a certain code language, “if FRIEND” is written as  “UIRVMW”, then how is “TRADER” will be written in that code language? 
Sol: The pattern used in this question is opposite to that letter such as

 Therefore, TRADER will be coded as GIZWVI. 

Example 3: If the word ‘EXAMINATION’ is coded as 56149512965, then the word ‘GOVERNMENT’ is coded as:
(a) 7645954552
(b) 7654694562
(c) 7645965426
(d) 7654964526
Sol: Option (a)
We are given that, ‘EXAMINATION’ = 56149512965
We can see that number places according to alphabetical order of E = 5, X = 24, A = 1, M = 13, I = 9, N = 14, T = 20, O = 15.
We can see the pattern as if the number > 9, then sum of the digit is assigned to that letter.
If the number place < 9, the number place is assigned to that letter.
In GOVERNMENT, G = 7, O = 1+5 = 6, V = 2+2 = 4, E = 5, R = 1+8 = 9, N = 1+4 = 5, M = 1+3 = 4, E = 5, N = 1+4 = 5, T = 2+0 = 2
Therefore, the code for ‘GOVERNMENT’ = 7645954552.
Hence, option A is the correct answer.