Out of the 40, 40 x 1/10 = <<40*1/10=4>>4 students are absent.
So, 40 - 4 = <<40-4=36>>36 students are present in school.
Out of the 36, 36 x 3/4 = <<36*3/4=27>>27 students are in the classroom.
This means, 36 - 27 = <<36-27=9>>9 students are in the canteen.
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