A mother decides to teach her son about a letter each day of the week. She will choose a letter from the name of the day. For example, on Saturday she might teach about the letter S or the letter U, but not the letter M. What letters are possible to teach using this method? (There are 15.) List all the letters in alphabetical order, with no spaces

A, D, E, F, H, I, M, N, O, R, S, T, U, W, Y

Explanation:

Order the letters of each day, omitting the repetitions:

MONDAY:

A, D, M, N, O, Y

TUESDAY:

A, D, E, S, T, U, Y

WEDNESDAY:

A, D, E, N, S, W, Y

THURSDAY:

A, D, H, R, S, T, U, Y

FRIDAY:

A, D, F, I, R, Y

SATURDAY:

A, D, R, S, T, U, Y

SUNDAY:

A, D, N, S, U, Y

Put the letters together:

A, D, M, N, O, Y, A, D, E, S, T, U, Y, A, D, E, N, S, W, Y, A, D, H, R, S, T, U, Y, A, D, F, I, R, Y, A, D, R, S, T, U, Y, A, D, N, S, U, Y

Delete the repetitions:

A, D, M, N, O, Y, E, S, T, U, W, H, R, F, I.

Reorder:

A, D, E, F, H, I, M, N, O, R, S, T, U, W, Y ← answer

What’s the question?