Two fathers and two sons go fishing. The catch that day isn't good, so they only catch three fish. That happens to be their only supply of food, so they split it evenly, without cutting, slicing, or mauling any of the fish. How is this possible?
There are only three persons at the outset, so the three fish is divided equally with each person having one fish as his share.
To explain the apparent paradox more clearly, let us denote these persons as A, B and C; where B is the father of A and C is the father of B, that is, C is the grandfather of A.
Consequently, even if there are two fathers and two sons amongst A, B and C; in reality there are precisely three persons who went fishing in the first place.