Coding-Decoding Questions for AFCAT

Letter Shifting (Most Common Type)

A word is coded by moving each letter forward or backward in the alphabet by a fixed number of steps. Think of the English alphabet as a circular track with 26 positions. If A=1, B=2 ... Z=26, then shifting CAT (+2) gives ECV. Always check the shift value first by comparing the original and coded letter. Shifts can be uniform (all letters same shift), alternating (+1/-1 for odd/even positions), or position-based.

• Alphabet positions: A=1, B=2, C=3 ... Z=26. Memorise this thoroughly.
• Uniform shift: every letter moves the same number of steps forward or backward.
• Alternating shift: odd-position letters shift one way, even-position letters another way.
• Reverse alphabet: A=26, B=25 ... Z=1. Opposite letter pairs: 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.
• Wrap-around rule: after Z comes A again (circular). Z+1 = A, Z+2 = B.
• Always check two or three letter pairs before concluding the shift value.

Word/Letter Reversal

The entire word is written in reverse order, or only specific parts are reversed. Sometimes the word is reversed and then shifted. This is easy to spot — write the coded word backwards and see if it matches the original. Always try reversal first before assuming a complex rule.

• Simple reversal: CAT coded as TAC. Write backwards to decode instantly.
• Reversal + shift: reverse the word first, then apply letter shifting.
• Sometimes only consonants are reversed while vowels stay, or vice versa.
• Check if reversed coded word directly gives the original — if yes, rule found in 5 seconds.

Number Coding (Letters Assigned to Numbers)

Each letter is replaced by a number based on a specific rule — could be its alphabetical position, its position from the reverse end, or an arbitrarily assigned code shown in a table. Questions either give you a code table to decode or ask you to identify the pattern from two examples.

• Position-based: A=1, B=2 ... Z=26 or reverse A=26, B=25 ... Z=1.
• Consecutive assignment: letters in a word are numbered 1,2,3 in order of appearance.
• Table/key based: a code table is given — just look up values, no pattern needed.
• Mixed format: e.g., BALL = 2+1+12+12 = 27. The code is the sum of positional values.
• Double-digit trick: sometimes the number 14 means N(14th letter), not 1 and 4 separately.

Symbol and Mixed Coding

Letters or words are replaced by symbols, digits, or a mix of both. The question gives 2-3 examples and asks you to decode a new word or identify the code for a specific word. The key technique is to find two coded words that share a common original letter — that shared symbol must be the code for that letter. Treat it like solving simultaneous equations.

• Compare two coded sentences that share a common word or letter to isolate individual codes.
• One-to-one mapping: each symbol always represents the same letter. Use this to narrow down.
• Eliminate known symbols to decode the remaining unknown letters.
• If 3 examples are given, you can usually decode any letter asked — just cross-reference.

Conditional and Odd-Position Coding

Some AFCAT questions give special conditions: vowels are coded one way and consonants another, or letters at odd positions shift differently from even positions. Read the condition statement very carefully. These appear less often but are tricky if you miss the condition.

• Odd vs even position rule: check position of each letter separately before applying shift.
• Vowel vs consonant rule: identify all vowels (A,E,I,O,U) and consonants first, then code separately.
• Capital vs lowercase coding: rare in AFCAT but watch out.
• Always re-read the condition in these questions — one missed word costs the mark.

• Checking only the first letter pair to determine shift — always verify with at least two or three letters before finalising the rule.
• Forgetting the wrap-around: Z+1 is A, not 27. Aspirants code Z+2 as AB instead of B and get wrong answers.
• Confusing forward alphabet position (A=1) with reverse position (A=26) — always clarify which system is being used by testing against the coded example.
• In symbol coding questions, guessing instead of cross-referencing two given examples — always isolate codes systematically.
• Applying the same rule to all letters when the question uses an alternating rule (odd-position +2, even-position -1) — read the condition statement fully.

• CROW trick for opposite letters: C-X, R-I, O-L, W-D — wrong! Use the formula 27-N. Memorise the 13 pairs: 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. Think of them as a mirror: fold the alphabet in half and they pair up face-to-face.
• EJOTY shortcut for alphabet positions: E=5, J=10, O=15, T=20, Y=25. Use these anchor points to count quickly instead of reciting A-B-C every time.
• 3-step method for any coding question: SPOT the pattern (compare original and code), CONFIRM with a second pair, APPLY to the new word. Never skip Confirm.
• For symbol coding, think of it as Sudoku — eliminate what you know to find what you don't. Two sentences sharing one word give you that word's code for free.

• AFCAT typically asks 2-4 Coding-Decoding questions per paper. These are usually straightforward letter-shift or reversal types — expect 1-2 easy questions and 1 slightly tricky conditional question.
• Time target: 30-45 seconds per question. If you spend more than 60 seconds on one, mark and move on — do not let these drain time from other sections.
• AFCAT rarely tests complex multi-condition codes. Most PYQ patterns are: single uniform shift, opposite letter substitution, and number-sum coding. Master these three and you cover 80 percent of what appears.
• In AFCAT 2 (EKT) papers for technical branches, number coding based on binary or alphanumeric patterns can appear — non-EKT AFCAT 1 stays to simple letter codes.
• Always use the EJOTY anchor (E=5, J=10, O=15, T=20, Y=25) during the exam — it cuts calculation time in half and reduces position-counting errors under pressure.