Initial Setup: The English Alphabet

The standard English alphabet contains 26 letters: A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z.

Identifying Letters for Deletion

The task requires deleting every third letter from the alphabet sequence:

• The 3rd letter is C.
• The 6th letter is F.
• The 9th letter is I.
• The 12th letter is L.
• The 15th letter is O.
• The 18th letter is R.
• The 21st letter is U.
• The 24th letter is X.

In total, 8 letters are removed based on this pattern.

Forming the New Alphabet Series

Removing the identified letters (C, F, I, L, O, R, U, X) results in a new sequence:

A, B, D, E, G, H, J, K, M, N, P, Q, S, T, V, W, Y, Z.

The length of this new series is $26 - 8 = 18$ letters.

Finding the Ninth Letter from the Right

To find the ninth letter from the right end of the new 18-letter series, we can count backwards from Z:

• 1st from right: Z
• 2nd from right: Y
• 3rd from right: W
• 4th from right: V
• 5th from right: T
• 6th from right: S
• 7th from right: Q
• 8th from right: P
• 9th from right: N

Alternatively, the ninth letter counting from the right is equivalent to the $(18 - 9 + 1) = 10$th letter counting from the left.

In the sequence A, B, D, E, G, H, J, K, M, N, P, Q, S, T, V, W, Y, Z, the 10th letter is indeed N.