Since the black dog weighs 1 pound more than the brown dog, the black dog weighs 1 + 4 = <<1+4=5>>5 pounds.
The white dog weighs 4 * 2 = <<4*2=8>>8 pounds.
Because the grey dog weighs 2 pounds less than the black dog, the grey dog weighs 5 - 2 = <<5-2=3>>3 pounds.
The total weight of all dogs is 4 + 5 + 8 + 3 = <<4+5+8+3=20>>20 pounds.
The average weight of all the dogs is 20 / 4 = <<20/4=5>>5 pounds.
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