Two Fathers and Two Sons Leaving Town

Classic Problem

Two fathers and two sons leave town.

This reduces the population of the town by three.

Solution

This is an instance of the riddle Two Fathers and Two Sons who are Three People.

The $3$ people involved are grandfather, father and son.

Historical Note

Eugene P. Northrop opens his Riddles in Mathematics of $1944$ with this riddle.

He takes care to categorise it as a paradox.

It is another instance of the Three Pheasants riddle, which appears in a work of Niccolò Fontana Tartaglia dating from the mid-$16$th century.

Sources

• 1944: Eugene P. Northrop: Riddles in Mathematics ... (next): Chapter One: What is a Paradox?