If 50 students came from Know It All High School, then Karen High, which had 3/5 times as many students as Know It All High School, had 3/5*50 = 30 students at the fair.
The total number of students from Know It All and Karen high schools is 50+30 = <<50+30=80>>80 students.
If Novel Corona had twice the combined number of students from Know It All and Karen high schools, then it had 2*80 = <<2*80=160>>160 students at the competition.
The total number of students at the competition is 80+160 = <<80+160=240>>240
#### 240