Its 2,9 because thats the highest it gets which is the maximum
There are 26 letters in the alphabet, 5 are vowels, therefore, the probability of choosing a vowel the first time is:

and the second time is:

Continuing with this reasoning, we get that the probabilities each time are:

Finally, the probability that you get all vowels is the product of the probabilities:

Writing the above result as a percentage we get:

Answer:
The square root of 36 is 6