In the second anthill, there are 20/100 * 100 = <<20/100*100=20>>20 ants less.
This means there are 100 - 20 = <<100-20=80>>80 ants in the second anthill.
In the third anthill, there are 20/100 * 80 = <<20/100*80=16>>16 ants less compared to the second one.
So in the third anthill, there are 80 - 16 = <<80-16=64>>64 ants.
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