Gregg has a bag containing 20 letter tiles corresponding to the first 20 letters in the alphabet. If Gregg selects one letter tile from the bag at random, what is the probability that he will select a vowel? Express your answer as a fraction in lowest terms.
There are 5 vowels in the English alphabet: A, E, I, O, U.
Therefore, the probability of selecting a vowel is 5/20 = 1/4.
So, the probability that Gregg will select a vowel is 1/4.