A letter is all you need to solve today's Think Thursday challenge at the mentalfloss.com Brain Game. Good luck!

What's the missing letter in the following group? And why?

C, D, I, L, M, ?, X

Here is the SOLUTION.

THE SOLUTION:

The missing letter is V.

The letters represent each of the Roman numeral digits in alphabetical order:
C = 100, D = 500, I = 1, L = 50, M = 1000, V = 5, X = 10.

Thanks for playing!