2/3 students are girls because 1 - (1/3) = 2/3
20 students are girls because 30 x (2/3) = <<30*(2/3)=20>>20
40% of the girls don't have any pets because 100 - 40 - 20 = <<100-40-20=40>>40
8 girls in class have no pets because 20 x .4 = <<20*.4=8>>8
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