If there were twice as many girls as boys present that day, then the number of boys is 140 girls / 2 girls/boy = <<140/2=70>>70 boys.
The total number of students present that day is 140 girls + 70 boys = <<140+70=210>>210 students.
If the class has 250 students, then the number of boys absent is 250 students - 210 students = <<250-210=40>>40 boys.
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