question: At a certain grade level, three-fourths of students have a desktop computer at home. If 20 students do not have desktop computers, how many students are there at that grade level?
answer: Twenty students represent 1 - 3/4 = 1/4 of the students at that level.
  So, there are 4 x 20 students = <<4*20=80>>80 students at that level.
  #### 80