Introduction: coding decoding reasoning
Almost every test of reasoning contains questions on coding. In such questions, generally one word and its code are given, and the students are required to find the code for the other word. The student is required to apply the same logic, as was applied in the given words.
Let's discuss some of the commonly asked questions based on coding:
Some of the major types of coding logics are

• Constant addition in the position of letters.
• Constant subtraction in the position of letters.
• Denoting the position of letters in the whole alphabetical order.
• Addition of the positions of all the letters to make code for the word.
• Constant addition and subtraction alternatively in the position of all the letters.
• Square of the number of letters in the word.
• Arranging the letters in the alphabetical order.
• Arrangement of letters in the word given in reverse order.
• Interchanging each pair of the letters, in the given word.
• Constant addition and then reversal of the letters to form the final word.

Now we will discuss some of the important types of coding with the help of examples.
Note: It is advised that the student should learn the alphabetical order of all the letters.
Some important coding decoding tricks & tips
The following method can be employed to learn the alphabetical order.
THE ALPHABET & EJOTY CONCEPT:
There are exactly 26 letters in English alphabets.
A-Z- (1 to 26),
A-1,
B-2;
C-3,  … and so on.

We should learn numbering of every letter. So for better convenience, you can learn two words which help you to remember numbering of letters which are given below:
A    B    C    D    E
F    G    H    I    J
K    L    M    N    O
P    Q    R    S    T
U    V    W    X    Y
          Z         

 5  10  15  20  25
 E  J   O   T   Y

Reverse EJOTY:
When we start count Alphabets from the Z to A, this is called reverse EJOTY.
It can be easily explained by an example given below:
Example:
If code for AYNA is ‘ZBMZ’, find the code for NUTS.
According to alphabet series, the position of A-1 , Y-25, N-14, A-1
In reverse EJOTY, Z-1, B-25, M- 14, Z-1
Or we can also say that,

    125141

    AYNA

    +

    ZBMZ

    2621326

Sum of every letter & its corresponding coded letter is 27. Therefore, code for NUTS is ‘MFGH’.

Types of Coding - Decoding

Type 1: Letter Coding.

Type 2: Number Coding.

Type 3: Substitution.

Type4: New Type of Coding
Detailed Explanation

Type 1: Letter Coding:

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.

Case-1: To form the code for another word

If in a certain language MYSTIFY is coded as NZTUJGZ, how is NEMESIS coded in that language?

Sol. Clearly, each letter in the word MYSTIFY is moved one step forward to obtain the corresponding letter of the code.

M Y S T I F Y

+1↓

N Z T U J G Z

So, in NEMESIS, N will be coded as O, E as F, M as N and so on. Thus, the code becomes OFNFTJT.

Case 2: To find the word by analyzing the given code (DECODING)

If in a certain language CARROM is coded as BZQQNL, which word will be coded as HOUSE?

SOL: each letter of the word is one step ahead of the corresponding letter of the code

B Z Q Q N L H O U S E

+1↓

C A R R O M I P V T F

So, H is coded as I, O as P, U as V, S as T and E as F. HOUSE is coded as IPVTF.

Type 2: NUMBER CODING

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

Case 1: When numerical code values are assigned to words

If in a certain language A is coded as 1,B is coded as 2, and so on, how is BIDDIC is coded in that code?

SOL:

As given the letters are coded as

A B C D E F G H I

1 2 3 4 5 6 7 8 9

So in BIDDIC, B is coded as 2, I as 9,D as 4 and C as 3. Thus, BIDDIC is coded as 294493

Case 2: Number to letter coding.

In a certain code, 2 is coded as P, 3 as N, 9 as Q, 5 as R, 4 as A and 6 as B. How is 599423 coded in that code?

SOL: Clearly as given 5 is coded as R, 9 as Q, 4 as A, 2 as P, 3 as N. So, 599423 is coded as RQQAPN

Type 3: SUBSTITUTION

In this section an object names are substituted with different object names. We should carefully trace the substitution and answer 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 color of human blood?

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

Type 4: NEW TYPE OF CODING

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.

For Example:

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

Sol: From the data we have T=@, O=$, M=*, E=? and A=•, R=£, E=?

Hence REMOTE is coded as £ ? * $ @ ?

Some Useful Tricks:

Trick 1: Use EJOTY to remember position of alphabet (Total=26) in series.

coding

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)

Trick 2: The reverse order can be obtained by subtracting the position from 27 say

Example: Opposite of M = 13 is 27-13= 14 = Four-teen = N