What is a coding-decoding question in reasoning tests?

These questions test pattern recognition — typically involving shifting letters in the alphabet, reversing words, or substituting letters/numbers according to a consistent rule.

A worked example

If "CAT" is coded as "DBU", how would "DOG" be coded?

Solution: Each letter shifts forward by one in the alphabet (C→D, A→B, T→U). Applying the same shift to DOG: D→E, O→P, G→H, giving "EPH".

Common coding patterns

• Letter shifting: each letter moves a fixed number of steps forward or backward in the alphabet
• Number substitution: letters are replaced with their position in the alphabet (A=1, B=2, etc.) or some variation
• Word/letter reversal: the code is simply the word spelled backward, or with letter pairs swapped

The key strategy is testing one letter or word at a time against the given example to isolate exactly what transformation rule is being applied, before applying it to the new word.