In the English alphabet, which letter lies exactly midway between the letters…

Concept: When the English alphabet is written out as A = 1, B = 2, C = 3, ... Z = 26, every letter has a fixed numeric position. The letter lying exactly midway between two given letters is the one whose position equals the average (mean) of the two letters' positions, since consecutive letters are equally spaced.

Application:

1. Locate the position of each given letter: G is the 7th letter of the alphabet, and S is the 19th letter.

2. Add the two positions and divide by 2 to get the midpoint position: (7 + 19) ÷ 2 = 26 ÷ 2 = 13.

3. Identify the letter at position 13: counting A(1), B(2), ... M(13), the 13th letter is M.

Cross-check: Listing every letter from G to S — G, H, I, J, K, L, M, N, O, P, Q, R, S — gives 13 letters in total, with M as the 7th letter in that list: six letters (G, H, I, J, K, L) precede it and six letters (N, O, P, Q, R, S) follow it, confirming M sits exactly at the centre.

Hence, M is the letter that lies exactly midway between G and S.