Coding Decoding – Concepts for Aptitude

Coding and Decoding is a critical topic in reasoning aptitude tests. It evaluates a candidate’s logical reasoning, pattern recognition, and ability to understand hidden relationships between elements (typically letters or numbers). In coding-decoding, a word, sentence, or a series of letters and numbers is coded in a particular way, and the objective is to decode it based on the given rules or find the code for a new word.

Types of Coding-Decoding

  1. Letter Coding
  2. Number Coding
  3. Substitution Coding
  4. Symbol Coding
  5. Mixed Letter-Number Coding

Let’s go over each type with examples and explanations.

1. Letter Coding

In letter coding, each letter in a word is replaced by another letter according to a certain rule. The pattern may involve shifting letters forward or backward in the alphabet, reversing positions, or alternating positions.

Example 1: Question: In a certain code, ROAD is written as URDG. How is MIND coded?

Solution:

  1. Observe the relationship between the letters:
    • R → U (+3), O → R (+3), A → D (+3), D → G (+3).
  2. So, each letter is shifted three places forward in the alphabet.
  3. Apply the same pattern to MIND:
    • M → P, I → L, N → Q, D → G.
  4. Answer: MIND is coded as PLQG.

Example 2: Question: If CAT is coded as DBU, how is DOG coded?

Solution:

  1. Identify the transformation:
    • C → D (+1), A → B (+1), T → U (+1).
  2. Each letter is increased by one.
  3. Applying the same to DOG:
    • D → E, O → P, G → H.
  4. Answer: DOG is coded as EPH.

2. Number Coding

In number coding, each letter or word is assigned a specific number. The pattern could be based on alphabetical positions, addition or subtraction of digits, or a specific rule applied to each letter or the entire word.

Example: Question: In a code language, APPLE is coded as 50. How is ORANGE coded?

Solution:

  1. Analyze how the code for APPLE could be derived:
    • Alphabetic positions: A = 1, P = 16, P = 16, L = 12, E = 5.
    • Sum of positions: 1 + 16 + 16 + 12 + 5 = 50.
  2. Apply the same to ORANGE:
    • O = 15, R = 18, A = 1, N = 14, G = 7, E = 5.
    • Sum of positions: 15 + 18 + 1 + 14 + 7 + 5 = 60.
  3. Answer: ORANGE is coded as 60.

3. Substitution Coding

In substitution coding, certain words are substituted with other words or numbers. The goal is to decode a sentence based on these substitutions.

Example: Question: In a certain code:

  • “Sky is blue” is written as “go la me,”
  • “Ocean is vast” is written as “ru la ti,”
  • “Sky and ocean” is written as “go ti ne.” What is the code for “is”?

Solution:

  1. Observe the sentences and look for common words:
    • “Sky is blue” → “go la me”
    • “Ocean is vast” → “ru la ti”
    • “Sky and ocean” → “go ti ne”
  2. The word “is” is common in the first two sentences and is represented by “la.”
  3. Answer: The code for “is” is la.

4. Symbol Coding

In symbol coding, each symbol represents a number or letter. The code may involve special characters (like @, #, $, etc.), and understanding the rule requires mapping each symbol to its corresponding number or letter.

Example: Question: In a certain code, the symbols @, #, $, and % represent 2, 4, 6, and 8, respectively. How would you code “48” using this symbol language?

Solution:

  1. Observe the codes given:
    • represents 4.
    • % represents 8.
  2. So, “48” would be coded as #%.

5. Mixed Letter-Number Coding

Mixed letter-number coding combines letters and numbers with a specific rule. The challenge often lies in figuring out how letters and numbers interact or follow a sequence.

Example: Question: In a code, HELLO is written as 8-5-12-12-15. How would you code WORLD?

Solution:

  1. Observe that each letter in HELLO is replaced by its alphabetical position:
    • H = 8, E = 5, L = 12, L = 12, O = 15.
  2. Apply the same to WORLD:
    • W = 23, O = 15, R = 18, L = 12, D = 4.
  3. Answer: WORLD is coded as 23-15-18-12-4.

Tips for Solving Coding-Decoding Questions

  1. Identify Consistent Patterns: Look for arithmetic changes (like +1, -2) between letters or numbers in the code.
  2. Use Alphabet Positions: Knowing letter positions (A = 1, B = 2, etc.) can be helpful, especially in letter coding.
  3. Break Down Complex Codes: If the coding rule is not obvious, try breaking down the code into smaller parts.
  4. Focus on Common Words: In substitution coding, find common words in multiple sentences to map them to the correct code.

Practice Questions

  1. Letter Coding: In a code, PAST is written as QBTC. How is STAR written?
  2. Number Coding: If GIRL is coded as 42, find the code for BOY.
  3. Substitution Coding: If “I love books” is coded as “mi la pa,” and “I love learning” is coded as “mi la ri,” what is the code for “books”?
  4. Symbol Coding: In a code, ! = 1, @ = 2, # = 3, and $ = 4. How is “3412” written?
  5. Mixed Letter-Number Coding: In a code, NICE is written as 14-9-3-5. What is the code for LOVE?

Solutions to Practice Questions

  1. Answer: UTBS (Each letter is shifted +1).
  2. Answer: 42 (B = 2, O = 15, Y = 25; Sum = 2 + 15 + 25 = 42).
  3. Answer: pa (Books appears only in the first sentence).
  4. Answer: #$@! (3, 4, 2, 1).
  5. Answer: 12-15-22-5 (L = 12, O = 15, V = 22, E = 5).

Read concepts and formulas for: Data Sufficiency

Refer Aptitude Questions with Solutions on Coding Decoding: https://www.learntheta.com/aptitude-questions-coding-decoding/

Practice Aptitude Questions on Coding Decoding with LearnTheta’s AI Practice Platform: https://www.learntheta.com/placement-aptitude/

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