Please enjoy the Think Thursday challenge from the mental_floss Brain Game. Good luck!

When writing out all the numbers from
ONE to ONE-HUNDRED (in English, of course)
which letter of the alphabet is only used TWICE?

Here is the SOLUTION.

THE SOLUTION:

The letter L.

It only appears in the numbers ELEVEN and TWELVE.

NOTE: The letter D also works here, as our clever readers pointed out, since it's used twice in ONE HUNDRED.