There were 100 people in attendance at the school dance.  Ten percent of the attendees were school faculty and staff.  Of the remaining attendees, two-thirds were girls.  How many boys attended the school dance?
Of 100 people in attendance at the school dance, 10% were school faculty and staff, or a total of 0.1*100=<<100*0.1=10>>10 people.
This leaves 100-10=<<100-10=90>>90 students in attendance.
Of the remaining attendees, two-thirds were girls, or (2/3)*90=<<(2/3)*90=60>>60 attendees were girls.
Thus, the remaining 90-60=<<90-60=30>>30 students were boys who attended the school dance.
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