In a certain code language, ‘RETAINED’ is written as ‘ENIATERD’ and ‘MATURITY’ is written as ‘TIRUTAMY’. How will ‘FIREWALL’ be written in that language?

Correct — C. Rule: the last letter stays put and the first seven are written in reverse order.

RETAINED: hold the final D, reverse RETAINE to ENIATER, then add D — ENIATERD.

MATURITY: hold the final Y, reverse MATURIT to TIRUTAM, then add Y — TIRUTAMY.

FIREWALL: hold the final L, reverse FIREWAL to LAWERIF, then add L — LAWERIFL, option (c).

Why the others are wrong

• (a)
  LAWEFIFR — LAWEFIFR cannot be right whatever the rule is: it holds two F's and one L, while FIREWALL holds one F and two L's. A rearrangement never changes which letters are present.
• (b)
  FLIREWAL — FLIREWAL simply lifts the final L into second place and leaves FIREWA in order. Nothing is reversed, so neither RETAINED nor MATURITY would come out as the paper prints them.
• (d)
  FLLAWERI — FLLAWERI freezes the first letter and reverses the other seven. That is the mirror of the actual rule, which freezes the last letter.

Two worked examples are enough to pin down a positional code if you look for what does not move.

In both examples the eighth letter of the code is the eighth letter of the word — D stays D, Y stays Y. Everything before it is the first seven letters read backwards.

Codes of this family are positional, not alphabetical. No letter changes identity, so the answer must be an anagram of the original word, which is a cheap first filter on the options.

Key facts

• RETAINED becomes ENIATERD by reversing the first seven letters and holding D in place.
• The code is always an anagram of the original word, so an option with a different letter count is out.
• FIREWALL contains one F and two L's, a test option (a) fails.

Common traps

• Reversing the whole word, which gives LLAWERIF.
• Freezing the first letter instead of the last.
• Skipping the anagram check and reading past option (a).

No directly related past PYQ was found.