In the English alphabet, the first 4 letters are written in opposite order; and the next 4 letters are written in opposite order and so on; and at the end Y and Z are interchanged. Which will be the fourth letter to the right of the 13th letter ?

(a) N
(b) T ✓ UPSC's answer
(c) H
(d) I

Why the answer is (b)

• The alphabet is rearranged in blocks of four in reverse order: A-D becomes D-C-B-A, E-H becomes H-G-F-E, I-L becomes L-K-J-I, M-P becomes P-O-N-M, Q-T becomes T-S-R-Q, U-X becomes X-W-V-U, and Y-Z becomes Z-Y.

• The resulting sequence is: D, C, B, A, H, G, F, E, L, K, J, I, P, O, N, M, T, S, R, Q, X, W, V, U, Z, Y.

• The 13th letter in this new sequence is P.

• Counting four letters to the right of P: the 14th is O, the 15th is N, the 16th is M, and the 17th is T.

• Therefore, the fourth letter to the right of the 13th letter is T.

Why the other options are wrong

(a) N: N is the 15th letter in the sequence, which is only the second letter to the right of the 13th letter (P).
(c) H: H is the 5th letter in the sequence, which is to the left of the 13th letter, not to the right.
(d) I: I is the 12th letter in the sequence, which is immediately to the left of the 13th letter (P).

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2021, held on 10 October 2021. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.