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3.3 Coding-Decoding
Pakistan Air Force GD Pilot Initial Test Exam
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1 Chapter 1: Introduction & Exam Overview
1.1 Current Exam Facts 1.2 Eligibility & Registration 1.3 Test Format & Selection Pipeline
2 Verbal Intelligence: Word Relationships
2.1 Analogies 2.2 Synonyms & Antonyms 2.3 Vocabulary in Context 2.4 Sentence Completion
3 Verbal Intelligence: Series & Coding
3.1 Number Series 3.2 Letter & Alpha-Numeric Series 3.3 Coding-Decoding
4 Verbal Intelligence: Quantitative Logic
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5 Non-Verbal Intelligence: Patterns
5.1 Pattern & Figure Series 5.2 Odd-One-Out 5.3 Classification
6 Non-Verbal Intelligence: Spatial Reasoning
6.1 Rotation 6.2 Mirror Images 6.3 Matrix Reasoning 6.4 Spatial Reasoning
7 English: Grammar Foundations
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8 English: Voice, Reported Speech, Correction & Vocabulary
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9 Physics: Mechanics & Fluids
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10 Physics: Waves, Optics & Modern
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11 Physics: Electromagnetism & Thermodynamics
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12 Mathematics: Algebra, Calculus & Logs
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13 Mathematics: Geometry, Trig, Matrices & Vectors
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14 Mathematics: Applied Reasoning
14.1 Percentages & Ratio 14.2 Word Problems
15 General Knowledge: PAF & Aviation
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16 General Knowledge: Pakistan & General Science
16.1 Pakistan Geography 16.2 Armed Forces Selection & Basic Science
17 Test-Day Strategy & Selection Pipeline
17.1 Test-Day Strategy 17.2 Later Selection Stages
3.3 Coding-Decoding
Key Takeaways Explain This Topic AI
Align the plain word and its code letter-by-letter to extract the mapping before applying it
Reverse alphabet coding uses the formula: reverse position = 27 − original position
Check whether the code is value-based (same letter → same digit) or positional (depends on word position)
For shift coding, verify the direction: +N means forward (A→C for +2), −N means backward
- Always verify the mapping is consistent across every letter of the given example before applying it
- Last updated: August 2026
3.3 Coding-Decoding
Quick Answer: Coding-decoding items give you a word and its coded form, then ask you to code another word using the same rule. The rule may be a letter shift, reverse alphabet, or letter-to-number substitution. Map each letter to its code symbol, then apply the mapping to the target word.
Coding-decoding is useful verbal-intelligence practice, but PAF does not publish a detailed public item-type blueprint. Each item presents a pair — a plain word and its coded form — and asks you to extend the same rule to a new word.
- The Four Main Coding Types
- 1. Letter Shift Coding
Each letter is shifted by a fixed number of positions.
Example: CAT → DBU (each letter +1: C→D, A→B, T→U).
- 2. Reverse Alphabet Coding
- Each letter is replaced by its mirror position: A↔Z, B↔Y, C↔X, …
Formula: reverse position = 27 − original position .
Example: DOG → WLT (D=4→23=W, O=15→12=L, G=7→20=T).
3. Number Coding of Words
Each letter is replaced by a digit given by the example's mapping.
Example: FELLOW = 465531 . Here the example itself defines the mapping F=4, E=6, L=5, O=3, W=1; you then apply that same mapping to the target word.
4. Mixed / Substitution Coding
The rule combines multiple operations — e.g., shift then reverse, or code the first half of the word one way and the second half another. These are rarer but appear on harder items.
Step-by-Step Method
Write the plain word and the coded form aligned , letter by letter (or letter-group by letter-group).
Extract the mapping — for each letter, note what it becomes. If the code is numeric, note which digit(s) correspond to which letter.
Check for a positional rule — is the code the same for the same letter wherever it appears? (If both L's in FELLOW map to 5, the rule is consistent letter-to-symbol, not position-dependent.)
Apply the mapping to the target word, letter by letter.
Verify — re-read the extracted mapping and confirm each letter of the target word has a defined code.
Worked Example 1 — Number Coding
Given: FELLOW = 465531 .
Question: How is ELLOW coded?
Step 1 — align and extract:
- F E L L O W
- 4 6 5 5 3 1
Mapping: F=4, E=6, L=5, O=3, W=1.
Step 2 — apply to ELLOW: E=6, L=5, L=5, O=3, W=1 → 65531 .
Worked Example 2 — Letter Shift
Given: CAT = DBU (shift +1).
Question: How is DOG coded?
Step 1 — extract the rule: C→D (+1), A→B (+1), T→U (+1). The rule is "shift each letter forward by 1."
Step 2 — apply: D→E, O→P, G→H → EPH .
Worked Example 3 — Reverse Alphabet
Given: A = Z, B = Y (reverse alphabet).
Question: How is DOG coded?
- D = 4 → 27 − 4 = 23 = W
- O = 15 → 27 − 15 = 12 = L
- G = 7 → 27 − 7 = 20 = T
Answer: WLT .
Worked Example 4 — Shift by +2
Given: WATER = YCVGT (each letter +2).
Question: How is FIRE coded?
- F + 2 = H
- I + 2 = K
- R + 2 = T
- E + 2 = G
Answer: HKTG .
Traps to Avoid
Positional vs value coding — some codes depend on the letter's position in the word (first letter → 1, second → 2, …), not on the letter's identity. If the same letter maps to different digits in different positions, suspect a positional rule.
One-to-many mappings — occasionally a single letter maps to a two-digit number (e.g., L = 12 → "12"). When concatenating, the coded string can be ambiguous (is "12" one letter or two?). Use the given example to disambiguate: if FELLOW = 465531 has six digits for six letters, each letter maps to exactly one digit.
Direction confusion — a "+2 shift" means forward (A→C); a "−2 shift" means backward (C→A). Misreading the direction is the most common single error.
Inconsistent case — treat upper and lower case identically. 'd' and 'D' both equal 4.
Mixed rules within one word — some items code the first half with one rule and the second half with another. If the standard shift doesn't fit the whole word, check whether the rule changes at the midpoint.
Speed Tips
For shift coding, count on your fingers if needed — it's fast and reliable for small shifts.
For reverse alphabet, use 27 − position rather than counting from Z.
Always verify the mapping is consistent across every letter of the given example before applying it; one misread letter invalidates the whole answer.