Question:  Dulwich College is a member of an association of how many independent schools?
Sentence (from "Headmasters' and Headmistresses' Conference"): The Headmasters' and Headmistresses' Conference (HMC) is an association of the headmasters or headmistresses of 283 independent schools (both boarding schools and day schools) in the United Kingdom, Crown dependencies and the Republic of Ireland.
Relevant evidence: Yes