Coding-Decoding

Coding-Decoding is a topic where a word or number is written in a secret language (code) and you have to find the logic behind it to decode other words. It is like cracking a secret message!

In SSC CGL, 2 to 3 questions are asked from this topic every year.

Types of Coding-Decoding in SSC CGL:

1. Letter Coding Each letter of a word is replaced by another letter based on a fixed rule.

Example: 
If CAT is coded as FDW, how is DOG coded?

Logic: C+3=F, A+3=D, T+3=W. 
Each letter is shifted 3 positions forward. D+3=G, O+3=R, G+3=J

Answer: GRJ

2. Number Coding Letters are replaced by numbers.
 

Example: 
If A=1, B=2, C=3... then CAT = 3+1+20 = 24
 

Or positional coding: 
If CAT = 312 (reverse position C=3, A=1, T... wait, T=2 not possible) 
Always check the exact rule given in the question.
 

3. Symbol Coding Letters or words are replaced by symbols.
 

Example: If ROAD is coded as @#%$, then
R = @, O = #, A = %, D = $

Now, to find the code for DOOR:
D = $, O = #, O = #, R = @

So, DOOR = $##@
 

4. Word/Sentence Coding Whole words are given codes.
 

Example: 
"sky is blue" = "nil hai asman" 
"grass is green" = "hara hai ghaas" 
Then code for "is" = "hai"
 

5. Mixed Number Coding A combination of position, reverse position and operations.
 

Example: 
If ARMY = 1+18+13+25 = 57 
Then NAVY = 14+1+22+25 = 62
 

Most Common Patterns in SSC CGL:
 

• Each letter shifted forward by fixed number (+1, +2, +3)
• Each letter shifted backward by fixed number (-1, -2, -3)
• Letters replaced by opposite letters (A=Z, B=Y)
• Letters replaced by their position numbers
• Alternate letters swapped
• Word written in reverse
   

How to Solve Coding-Decoding Questions:
 

Step 1 - Look at the given coded word carefully. 
Step 2 - Write the position numbers of each letter. 
Step 3 - Compare original letters with coded letters. 
Step 4 - Find the pattern - is it +1, +2, -1, reverse or something else? 
Step 5 - Apply the same pattern to the new word.
 

Important Tips:

• Always check both forward (+) and backward (-) shift
• If shifting does not work, check if letters are reversed
• In number coding, check if numbers are positions or reverse positions
• Practice 15 questions daily from this topic
• In sentence coding, find the common word in two sentences - its code will be the common code word