7th Class Mathematics Coding-Decoding CODING-DECODING


Category : 7th Class

Learning Objectives:

  • To learn of conveying a message through signals.
  • To learn how to decode a signal given in the form of codes.



A 'code' is a system of conveying a message through signals. It is a method of sending a message between sender and receiver in such a way that only sender and receiver can know its meaning. However 'coding' is done according to a certain pattern in the mind of the sender. Therefore its meaning cannot be deciphered by a third person. Only if he carefully studies this pattern, he can decode it. This process is called 'Decoding'. This capability is important in many fields of application like computer programming, military applications, etc.

The 'Coding-Decoding' test is set up to judge the candidates' ability to decipher the pattern which goes behind a coded message or statement. In questions on coding, artificial values are assigned to certain given words and the candidates are required to find out the code for another given word.





Letter coding: In such questions, code values are assigned to a word in terms of the alphabets. In this category, one word is coded according to a particular pattern and the candidate is asked to give the code letters for another word following the same pattern of coding.

Example 1:

If TEMPLE is coded as RCKNJC, in the same way MOSQUE is coded as

(a) KNQPTD                        (b) KMQOSC     

(c) OQUSWG                      (d) LMPNRB


(b) In the coded word TEMPLE, each letter has been moved in backward direction with a gap of 1 letter.


   \text{T} & \text{E} & \text{M} & \text{P} & \text{L} & \text{E}  \\

   -2\downarrow  & -2\downarrow  & -2\downarrow  & -2\downarrow  & -2\downarrow  & -2\downarrow   \\

   \text{R} & \text{C} & \text{K} & \text{N} & \text{J} & \text{C}  \\



In the same way MOSQUE is


   \text{M} & \text{O} & \text{S} & \text{Q} & \text{U} & \text{E}  \\

   -2\downarrow  & -2\downarrow  & -2\downarrow  & -2\downarrow  & -2\downarrow  & -2\downarrow   \\

   \text{K} & \text{M} & \text{Q} & \text{O} & \text{S} & \text{C}  \\


So (b) is the correct answer.


Example 2:

In a secret way of writing GANDHI WASAGREAT LEADER OF INDIA, it is written as RUFZOJSUV U RDTUB QTUZTD EP JFZJU. Keeping this in mind, pick the code for each word given below from the choices given:


(a) VBDERE       

(b) VBDEER    

(c) VBEDFR       


(e) None



(a) JVQUFZ                     

(b) ZFUQVJ     

(c)  QUFZJV                        


(e) None


(i) (d) VBDEFR. It is clear that codes for letters in STRONG will be

\[S\to V,T\to B,R\to D,O\to E,N\to F,G\to R.\]

(ii) (a) JVQUFZ. It is clear that codes for letters in ISLAND will be

\[I\to J,S\to V,L\to Q,A\to U,N\to F,D\to Z.\]



Numerical coding: In these questions numerical values are assigned to a word on a certain pattern and the candidates are required to analyses the code according to directions.

Example 1:

In a certain code language, the word 'GRATEFUL’ is coded as 90, how will the word 'CALCULATOR' be coded in the same pattern?

(a) 100                                  (b) 106           

(c) 90                                     (d) 116


(b) The word GRATEFUL is coded as per position of each letter in the English alphabet series like


 \text{G} & \text{R} & \text{A} & \text{T} & \text{E} & \text{F} & \text{U} & \text{L}  \\

   7+ & 18+ & 1+ & 20+ & 5+ & 6+ & 21+ & 12  \\





   \text{C} & \text{A} & \text{L} & \text{C} & \text{U} & \text{L} & \text{A} & \text{T} & \text{O} & \text{R}  \\

   \text{3+} & \text{1+} & \text{12+} & \text{3+} & \text{21+} & \text{12+} & \text{1+} & \text{20+} & \text{15+} & \text{18}  \\



Example 2:

In a certain code, BRAIN is written as \[*\text{ }%\div \#\,\times \] and TIER is written as\[\$\#\,+%\]. How is RENT written in that code?

(a) \[%\times \#\$\]                       (b) \[%\#\times \$\]

(c) \[%+\times \$\]                         (d) \[+\times %\,\$\]


(c) It is clear from the code language that the symbols for letters in the word 'RENT', will be

R                %

E                +

N                x

T                $

So (c) is the correct option.

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