Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2010/paper-2/17/b/solution

Every seven-element subset of the hundred individually identifiable tiles is equally likely. Choose three of the thirty-four vowels and four of the sixty-four consonants; the favourable draw has no blank tiles. Thus
This is a multivariate hypergeometric distribution count, including the implicit factor for blanks. Dividing by instead would incorrectly condition on having drawn no blanks.

New to topics? Read the docs here!