If the second half of the English alphabet (from N to Z) is written in reverse order while the first half remains the same, which letter will be fourth to the right of the twentieth letter from the right end in this new alphabet sequence?

Introduction / Context:
This question modifies only the second half of the alphabet and then asks you to find a letter based on relative positions from the right and left. It is another example of letter ranking with a twist involving partial reversal. Such problems appear frequently in aptitude tests because they require careful tracking of how transformations affect positions. Solving them strengthens your grasp of ordered sequences and relative indexing.

Given Data / Assumptions:
We begin with the standard English alphabet A to Z. The first half, letters A to M, are kept in the original order. The second half, letters N to Z, are written in reverse order. This produces a new sequence of 26 letters. In this new arrangement, we must first identify the twentieth letter from the right end. After locating that letter, we then move four positions to the right of it and find the letter at that position. The final answer must be one of U, K, E, F or Q.

Concept / Approach:
First construct the modified alphabet explicitly. A to M remain A, B, C, D, E, F, G, H, I, J, K, L, M. The second half from N to Z is reversed, so the right half becomes Z, Y, X, W, V, U, T, S, R, Q, P, O, N. Join these to form the new sequence. To find the twentieth from the right, convert that right based index to a left based index using the formula 26 minus 20 plus 1. Once we know its left index, we can easily move four positions to the right by adding four and reading off the corresponding letter.

Step-by-Step Solution:
Write the first half as is: A B C D E F G H I J K L M. Reverse the second half N to Z to get: Z Y X W V U T S R Q P O N. Combine both halves to form the new sequence: A B C D E F G H I J K L M Z Y X W V U T S R Q P O N. To find the twentieth letter from the right, convert to a left index: 26 - 20 + 1 = 7. The 7th letter from the left in the new sequence is G, since we count A(1), B(2), C(3), D(4), E(5), F(6), G(7). Now move four positions to the right of G: 7 + 4 = 11. The 11th letter in the new sequence is K, as the first 13 letters remain the original A to M, making K the 11th letter.

Verification / Alternative check:
For verification, you can count directly from the right end of the new sequence. From the right, the letters are N(1), O(2), P(3), Q(4), R(5), S(6), T(7), U(8), V(9), W(10), X(11), Y(12), Z(13), M(14), L(15), K(16), J(17), I(18), H(19), G(20). So G is indeed the twentieth letter from the right. From this G, moving four positions to the right (towards A) in the left to right direction takes us through H(8), I(9), J(10) and K(11). Both the index conversion method and the direct counting confirm that K is the desired letter. This double check removes any doubt about miscounting.

Why Other Options Are Wrong:
U lies in the reversed second half and appears near the middle of that half, not at the computed index 11. E and F are 5th and 6th from the left respectively and therefore do not match the required position four steps to the right of the twentieth from the right. Q appears much later in the new sequence and does not satisfy the positional relationship. Only K appears at the correct index after performing both steps of the calculation (finding the twentieth from the right and then moving four to the right). Hence all other options must be rejected.

Common Pitfalls:
One common mistake is to reverse the entire alphabet instead of only the second half, which completely changes the positions. Another pitfall is to miscalculate the conversion from right based position to left based position, often forgetting to add one after subtracting from 26. Some candidates also accidentally shift in the wrong direction when asked to move to the right of a given position. To avoid these errors, clearly write the modified sequence, use the right to left index conversion formula carefully and recheck the direction in which you move along the sequence. Taking a moment to double count from the right is a simple but effective safeguard.

Final Answer:
In the described modified alphabet, the letter that is fourth to the right of the twentieth letter from the right end is K.