There are twice as many penguins as giraffes, so there are 5 * 2 = <<5*2=10>>10 penguins.
The penguins make up 20% of all animals, so there are 100/20 * 10 = <<100/20*10=50>>50 animals in the whole Zoo.
4% of animals are elephants, so there are 4/100 * 50 = <<4/100*50=2>>2 elephants at the Zoo.
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