Coding and Decoding: Letter, Number/Mixed Number, Substitution based Coding and Decoding Formula and Tricks with Problem (Question) and Solutions

Type 1: Letter Coding

In this type of question the letter in a word is replaced by certain other letter according toa specific rule to fromits code.

Ex- The word ROAD is coded as URDG. What should be the code letters of SWAN?

Solution: Here,



∴ SWAN should be VZDQ.

Ex- In a certain code FAVOUR is written as EBUPTS. How is DANGER written in code?

Solution: Here,

Coding decoding


Coding decoding

DANGER will be coded as CBMHDS.

Ex- In a certain code MIRACLE is written as NKUEHRL. How will GAMBLE be written in the code.

Solution: Here,

Coding decoding


Coding decoding

Type 2: Number Coding

In this type of questions either numerical code values are assigned to a word or alphabetical code letters are assigned to the numbers. This type of coding involves two types of cases :

Ex- If C = 3 and COVER = 63, then BASIC = ?

Sol- Clearly, in the given code, A = 1, B = 2, C = 3, ….. so that

COVER = 3 + 15 + 22 + 5 + 18 = 63

∴ BASIC = 2 + 1 + 19 + 9 + 3 = 34.

Ex-If ABCNE can be coded as 3, 7,2, 9, 11 and OAPILB can be coded as 13,3,15,17,32,94 then BOI will be coded as


A=3, B=7, C=2, N=9, E=11

O=13, A=3, P=15, I=17, L=32, B=94

by comparing,




Type 3: Substitution Coding

In this type questions some particular words are assigned certain substituted names.

Ex- If ‘light’ is called ‘morning’, ‘morning’ is called ‘dark’, ‘dark’ is called ‘night’, ‘night’ is called ‘sunshine’ and ‘sunshine’ is called ‘dusk’, when do we sleep ?

(a) Night

(b) Sunshine

(c) Dusk

(d) Dark

Sol. (b) We sleep in the ‘night’. But ‘night’ is called ‘sunshine’. So, we sleep in the ‘sunshine’.

Type 4: Mixed letter coding

In this type of questions, three or more sentences are given in the coded language and the code for a particular word is asked. To find the code for the particular word, pickup two sentences bearing a common word and the common code word will mean that word. Proceeding in similar manner, we can be determined a particular code word for each word of given sentences.


Ex- In a certain code language, ‘ko ki to ma’ means ‘Rina is playing cricket’. ‘kp ja ki ma’ means ‘Bittu is playing badminton’. ‘ki tp sp ho’ Means ‘they are playing football’ and ‘ko su kp’ means ‘cricket and badminton’. Which word in that language means ‘Bittu’?


ko ki to ma → Rina is playing cricket    ——-eq.1
kp ja ki ma → Bittu is playing badminton    ——-eq.2 
ki tp sp ho → they are playing football   ——eq.3
ko su kpcricket and badminton    ——eq.4

  1. ho
  2. ma
  3. ja
  4. tp

Solution. (c): Comparing relation in each of the statement, we get Bittu is coded as ‘ja’.

Type 5: Coding by Combinations of Letters, Numbers or Symbols

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