# What is the next letter in the sequence?

What is the next letter in the sequence below?

T  D  Q  I  N  N  K  ?


Hints will come if needed.

Is it

S

Because

Adding the positions of each pair of letters creates an arithmetic progression i.e.
T and D = 20 + 4 = 24,
Q and I = 17 + 9 = 26,
N and N = 14 +14 = 28.
The next term is 30 and so the next letter is 30 - 11 = 19
i.e. S

• Well, you are right, but my reasoning was a little different: (WARNING, spoiler ahead): there are two sequences, a descending one (20, 17, 14, 11) and an ascending one (4, 9, 14, ?). The next element would be 19 for the ascending one, which is equivalent to S. Anyway, as the descending one has a delta of -3 and the ascending one has a delta of 5, the pairs result in an ascending sequence with delta = 2. – Chaotic May 28 '16 at 21:17