On the third day, 1/7*280 = <<1/7*280=40>>40 students called in sick.
If the number of students absent on the second day was twice the number on the third day, then 2*40 = <<2*40=80>>80 students didn't show up for the class on the second day.
The total number of students present in the class on the second day was 280-80= <<280-80=200>>200.
If 40 fewer students showed up for the class on the first day than on the second day, then 200-40 = <<200-40=160>>160 students showed up for the class on the first day.
The number of students absent on the first day is 280-160 = <<280-160=120>>120
In the three days, the total number of absentees is 120+80+40 = <<120+80+40=240>>240
#### 240