Out of 100 students, half are girls and half are boys so there are 100/2 = <<100/2=50>>50 girls
There are 50 girls out of 100 students means there are 100-50 = <<100-50=50>>50 boys
20% of the 50 girls have dogs so they have .20*50 = <<20*.01*50=10>>10 dogs
10% of the 50 boys have dogs so they have .10*50 = <<.10*50=5>>5 dogs
The girls have 10 dogs and the boys have 5 dogs so together, they have 10+5 = <<10+5=15>>15 dogs
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