If in a certain code, 'POT' is written as ATOP and 'TRAP' is written as APART, then how is 'ARENA' written in that code?

(a) AARENA
(b) AANREA
(c) AANEAR
(d) AANERA ✓ UPSC's answer

Why the answer is (d)

• Analyze the first example: 'POT' becomes 'ATOP'. The original letters are P, O, T. The code is A, T, O, P. This indicates the original string is reversed to T, O, P, and then 'A' is prepended to the front.

• Verify with the second example: 'TRAP' becomes 'APART'. The original letters are T, R, A, P. Reversing them gives P, A, R, T. Prepending 'A' to this reversed string results in A, P, A, R, T, which matches 'APART'.

• Apply the rule to 'ARENA': First, reverse the letters of 'ARENA' to get 'ANERA'.

• Next, prepend the letter 'A' to the reversed string 'ANERA'.

• The final coded string is 'A' + 'ANERA' = 'AANERA'.

• Therefore, the correct option is (d).

Why the other options are wrong

(a) AARENA: Option (a) 'AARENA' incorrectly keeps the original word order instead of reversing the letters before adding the prefix.
(b) AANREA: Option (b) 'AANREA' contains an incorrect sequence of letters that does not match the reverse of 'ARENA'.
(c) AANEAR: Option (c) 'AANEAR' has the last two letters 'AR' swapped compared to the correct reversed sequence 'ANERA'.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2024, held on 16 June 2024. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.