We use the complement rule of probability. P(at least one vowel) = 1 - P(no vowel) To solve for P(no vowel) = (4/6)(3/5) = 2/5; since there are 4 consonants out of 6 letters and we take the letters without replacement.
P(at least one vowel) = 1 - 2/5 = 3/5. The answer is B.