The letter tiles given are W, I, S, D, O, M.
First, let's identify the vowels among these letters. The vowels in the English alphabet are A, E, I, O, and U. In the given tiles, the vowels are:
- I
- O
So, there are 2 vowels.
Next, let's find the total number of letter tiles:
- Total tiles = 6 (W, I, S, D, O, M)
Now, we can calculate the probability of selecting a vowel. The probability \( P \) is given by the formula:
\[ P(\text{vowel}) = \frac{\text{Number of vowels}}{\text{Total number of tiles}} = \frac{2}{6} \]
We can simplify \( \frac{2}{6} \):
\[ \frac{2}{6} = \frac{1}{3} \]
Therefore, the probability that the letter Abby picks is a vowel is
\[ \boxed{\frac{1}{3}}. \]