Letter and word codes
Deduce a letter-substitution rule from an example and apply it.
What a code question asks
A code question gives a word and its coded form, then asks you to apply the same rule to another word — or to spot the one code that breaks the rule.
Finding the rule
Nearly every code at this level is one of a handful of rules:
- Shift — each letter moves a fixed number of places (CAT → DBU is +1)
- Reverse — the word is written backwards (CAT → TAC)
- Swap — letters exchange positions in a fixed pattern
- Substitute — letters map to numbers, often A=1, B=2
Work out the rule from the first letter only, then check it against the second. If it holds for two letters it almost certainly holds for the rest.
How to attack this question type
- 1
In EduTest you get NO working-out paper, so practise counting letter positions in your head — that is the real exam condition.
- 2
Check the first letter, then confirm with the second. Do not decode the whole word before you have a hypothesis.
- 3
For "which code is wrong", look for the palindrome trick: a word reading the same backwards is unchanged by a reverse code.
- 4
If a shift rule breaks at the end of the alphabet, remember it wraps: Z + 1 = A.
Practice · untimed
In a certain code, MAP is written as NBQ. How would DOG be written in the same code?