Maggie was allowed to take half of the goldfish in the aquarium, a total of 1/2*100 = <<1/2*100=50>>50 goldfish
On her first catch, Maggie got 3/5*50 = <<3/5*50=30>>30 goldfish.
To reach the number of goldfish she was allowed to take home, Maggie has to catch 50-30 = <<50-30=20>>20 more goldfish.
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