Coding-decoding is pure practice, like all of reasoning. No book can make you fast at it; only solving every type, many times, does. But you do need the right base. If you know the alphabet positions cold, most codes break in the first ten seconds.
What this topic covers
The base: alphabet positions
| A | B | C | D | E | F | G | H | I | J | K | L | M |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
| N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 |
- EJOTY: E = 5, J = 10, O = 15, T = 20, Y = 25. Count from the nearest anchor.
- Opposite letters: positions add up to 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.
- Reverse position of any letter = 27 − its position.
The four common patterns
- Letter shift: each letter moves forward or backward by a fixed number (+1, −2...), or by a changing number (+1, +2, +3...).
- Opposite letters: each letter is replaced by its opposite.
- Number codes: a word becomes a number, often the sum of positions, or each letter becomes its position.
- Word codes: sentences in a secret language; compare common words.
How it is asked in the exam
Example 1: letter shift
If CAT is coded as DBU, how is DOG coded?
C→D, A→B, T→U: every letter +1. So D→E, O→P, G→H: EPH.
Example 2: a longer shift
If MONKEY is coded as NPOLFZ, how is TIGER coded?
Every letter +1. T→U, I→J, G→H, E→F, R→S: UJHFS.
Example 3: opposite letters
In a code, HELLO is written as SVOOL. How is WORLD written?
H(8)→S(19), E(5)→V(22): 8 + 19 = 27, 5 + 22 = 27. Opposite letters. W→D, O→L, R→I, L→O, D→W: DLIOW.
Example 4: sum of positions
If PEN = 35, what is CAP?
P(16) + E(5) + N(14) = 35. So CAP = 3 + 1 + 16 = 20.
Example 5: word codes
In a code language, "sky is blue" is "ta na pa", "blue is good" is "pa ka na" and "good boy" is "ka ra". What is the code for "sky"?
- Sentences 1 and 2 share is and blue; their codes share na and pa.
- So the remaining word sky = the remaining code ta.
- Also: sentences 2 and 3 share good → ka, so boy = ra.
Example 6: check every letter
If ROAD is coded as URDG, how is SWAN coded?
R→U (+3), O→R (+3), A→D (+3), D→G (+3). So SWAN → VZDQ. Check the whole word, not just the first letter, before you choose. Many questions shift the first letter by one amount and the rest by another.
Points to remember
- Test the first two letters before deciding the pattern. One letter can match two different rules.
- When the code is the same length as the word, think shift or opposite. When it is a number, think positions.
- For word codes, a word that appears only once is solved last, by elimination.
- The alphabet wraps around in shift codes: Z + 1 = A.
Common mistakes
- Counting positions on your fingers in the exam. Learn EJOTY and the opposite pairs now, so this never happens.
- Forgetting the wrap-around (Y + 3 = B).
- In word codes, assuming the order of codes matches the order of words. It usually doesn't.
Practise straight after reading
Write the alphabet with positions and opposites from memory every day for a week. Then solve at least 20 questions of each of the four patterns from your reasoning book, and 100 to 200 mixed questions from the reasoning quizzes on this site. Mark every wrong answer with its pattern, and revise those after 1, 7 and 30 days.