In the word "MODELS," the vowel letters are 'O' and 'E'. There are a total of 6 letters in the word.
Since the probability model is uniform, each letter has the same probability of being selected, which is \( \frac{1}{6} \).
Now, to find the probability of selecting a vowel letter, we need to sum the probabilities of selecting 'O' and 'E':
\[ P(\text{vowel}) = P(O) + P(E) = \frac{1}{6} + \frac{1}{6} = \frac{2}{6} = \frac{1}{3} \]
Thus, the probability of selecting a vowel letter from the word "MODELS" is:
Start Fraction 1 over 3 End Fraction.