Coding-Decoding

Coding-Decoding

Overview

This topic tests your ability to identify hidden patterns in how letters, numbers, or symbols are transformed according to a specific rule. The examiner encodes a word using a particular logic, and you must crack that logic to decode new words or find the code for given words.

The beauty of this topic lies in its predictability—once you recognize the pattern type, solving becomes mechanical. However, the trap is overthinking simple patterns or missing subtle variations. Mastering coding-decoding requires pattern recognition speed rather than complex reasoning, making it an easy scoring area if you practice the common types systematically.

For SBI Clerk level, expect straightforward single-rule or two-rule patterns. The questions are designed to be solved in 30–45 seconds each, so quick identification of the coding logic is essential.

Key Concepts

• Letter Shifting: Each letter moves forward or backward in the alphabet by a fixed number (e.g., A→C means +2 shift). The shift can be uniform or positional (1st letter +1, 2nd letter +2, etc.).
• Reverse Order Coding: The letters of the word are simply written in reverse order, sometimes combined with a shift.
• Opposite Letter Coding: Each letter is replaced by its opposite in the alphabet (A↔Z, B↔Y, C↔X). Remember: Letter + Opposite = 27.
• Position-Based Coding: Letters are replaced by their alphabetical position numbers (A=1, B=2... Z=26) or vice versa.
• Symbol/Number Substitution: Letters are replaced by symbols or numbers following a consistent pattern across all given examples.
• Vowel-Consonant Rules: Different rules apply to vowels and consonants—vowels might shift +1 while consonants shift -1.
• New Pattern Coding: A sentence-based format where you deduce word-code pairs by comparing multiple coded sentences to find common elements.

Formulas / Key Facts

Alphabet Position Reference (memorize this):

• A=1, B=2, C=3... L=12, M=13, N=14... Z=26
• Quick check: E=5, J=10, O=15, T=20

Opposite Letter Pairs (sum = 27):

• A↔Z, B↔Y, C↔X, D↔W, E↔V, F↔U, G↔T, H↔S, I↔R, J↔Q, K↔P, L↔O, M↔N

EJOTY Technique: E=5, J=10, O=15, T=20, Y=25 — use these as reference points to quickly find any letter's position.

Forward/Backward Shift Rule: If shifting forward from Z, continue from A (cyclic). Z+2 = B.

Pattern Identification Order: First check reversal → then opposite letters → then uniform shift → then positional shift → then vowel/consonant rules.

Sentence Coding Logic: If two sentences share one common word and one common code, that code represents that word.

Worked Examples

Example 1: Letter Shifting

If COME is coded as DPNF, how is BACK coded?

Step 1: Compare each letter pair

• C→D (+1), O→P (+1), M→N (+1), E→F (+1)

Step 2: Pattern identified — each letter shifts +1

Step 3: Apply to BACK

• B+1=C, A+1=B, C+1=D, K+1=L

Answer: CBDL

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Example 2: Opposite Letter Coding

If TIGER is coded as GRTVI, how is LION coded?

Step 1: Check each letter

• T(20)→G(7): 20+7=27 ✓ (opposites)
• I(9)→R(18): 9+18=27 ✓
• G(7)→T(20): 7+20=27 ✓
• E(5)→V(22): 5+22=27 ✓
• R(18)→I(9): 18+9=27 ✓

Step 2: Pattern — opposite letters

Step 3: Apply to LION

• L(12)→O(15)? No, 12+15≠27. Opposite of L(12) is O(15)? Check: 12+15=27 ✓
• L→O, I→R, O→L, N→M

Answer: ORLM

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Example 3: New Pattern (Sentence-Based)

Given:

• 'sky is blue' → 'ra ta na'
• 'blue is bright' → 'na pa ta'
• 'bright sky high' → 'pa sa ra'

What is the code for 'blue'?

Step 1: Compare sentences 1 and 2

• Common words: 'is', 'blue'
• Common codes: 'na', 'ta'

Step 2: Compare sentences 2 and 3

• Common word: 'bright'
• Common code: 'pa'
• So 'bright' = 'pa'

Step 3: From sentence 2, remaining after removing 'bright/pa':

• 'blue is' = 'na ta'

Step 4: Compare sentences 1 and 3

• Common word: 'sky'
• Common code: 'ra'
• So 'sky' = 'ra'

Step 5: From sentence 1, removing 'sky/ra':

• 'is blue' = 'ta na'
• Since 'is' appears in sentences 1 and 2 with 'ta' common → 'is' = 'ta'

Answer: 'blue' = 'na'

Common Mistakes

• Assuming uniform shift without checking all letters → Always verify the pattern holds for every letter in the given example before applying.
• Forgetting cyclic nature of alphabet → When Z+3 is needed, count Z→A→B→C, answer is C, not stuck at Z.
• Confusing opposite letter calculation → Don't subtract from 26; the sum of positions equals 27. Opposite of C(3) is X(24) because 3+24=27.
• Rushing sentence-based coding → Carefully track which words appear in which sentences. Make a small table: write words in rows, sentences in columns, tick marks for presence.
• Ignoring reversal before shift → Some codes first reverse the word, then apply a shift. If direct shift doesn't work, try reverse+shift.

Quick Reference

• Opposite letters always sum to 27: A(1)+Z(26)=27
• EJOTY: E=5, J=10, O=15, T=20, Y=25 — your anchor points
• First check: Is it simply reversed? Then check opposite letters. Then check shifts.
• Positional shift pattern: 1st letter +1, 2nd letter +2, 3rd letter +3...
• Sentence coding: Find common word between two sentences = find common code
• When stuck, write out both alphabets (A-Z and Z-A) on rough sheet for quick reference