Coding-Decoding
Coding-decoding is a substitution cipher wearing a puzzle costume. Once you find the rule connecting one word to its code, apply the identical rule to the new word — nothing else is needed.
Mental model
Every coding question is a MAPPING, so make the mapping visible before you answer. Write the alphabet with its position numbers along the top of your rough sheet once, at the start of the paper — A is 1, Z is 26 — and never count letters again. Then classify: letter-shift (fixed +n or -n), position-arithmetic (letter turned into its number and operated on), reversal or rearrangement of the word, or substitution coding where whole words stand for whole words. Identify the class first; solving is mechanical afterwards.
Associations
A short trigger on the left, everything it pulls with it on the right.
Letter-shift, letter-reversal, number-substitution — the three families.
Letter-shift moves each letter forward or back a fixed number of places in the alphabet. Letter-reversal maps A to Z, B to Y, and so on. Number-substitution simply replaces each letter with its position number. Test all three against the given example before trying the new word.
Write the alphabet with position numbers before you start.
A=1 through Z=26, jotted once at the top of your scratch space, turns every shift-and-substitution question into simple addition or subtraction instead of mental alphabet-counting under time pressure.
Things to remember
The night-before list. Short enough to recall cold.
- 1In a simple forward shift cipher, each letter is replaced by the letter a fixed number of places later in the alphabet, wrapping from Z back to A.
- 2In a reversal cipher, A pairs with Z, B with Y, and generally a letter at position n pairs with the letter at position (27 - n).
- 3Coding can apply to whole words too — a rule might shift every word to the next word in a fixed sequence rather than acting letter by letter.
- 4Always derive the rule from the given example pair first; never guess the rule from the answer options.
In detail
- Letter positions: A=1 to Z=26. The reverse position of any letter is 27 minus its forward position, so N (14) has reverse position 13, which is M.
- The EJOTY handle fixes five anchor letters — E=5, J=10, O=15, T=20, Y=25 — so you can jump to any position in one step.
- In substitution coding ('if sky is called sea'), answer strictly by the new dictionary, never by real-world meaning — that is the intended trap.
- In coded-language questions with several sentences, find the one word common to two sentences and match it against the one code common to their codes; that single pairing unlocks the rest.
- Always check whether the shift is applied to the word in its given order or in reverse order before choosing the option; both options are usually present.
Where people slip
- Do not assume the shift amount without checking it against every letter of the given example — a rule that fits the first letter alone can still be wrong.
Check yourself
Nothing here is scored — it will not change your mastery figures.
If CAT is coded as DBU, how is DOG coded in the same pattern?
From the question bank
In a certain code, CAT is written as DBU (each letter of the alphabet is shifted forward by one place). How is DOG written in that code?
From the question bank
In a code, each letter is replaced by its position number in the alphabet (A=1, B=2, ... Z=26). 'GO' is written as '7 15'. How is 'SUN' written in this code?
Books to read
- A Modern Approach to Verbal and Non-Verbal Reasoning — R S Aggarwal
- Analytical Reasoning — M K Pandey
Official sources
Hand-checked official domains only — the notes above carry no links of their own.