Solution

(related to Problem: The Milkmaid Puzzle)

Draw a straight line, as shown in the diagram, from the milking-stool perpendicular to the near bank of the river, and continue it to the point $A,$ which is the same distance from that bank as the stool. If you now draw the straight line from $A$ to the door of the dairy, it will cut the river at $B.$ Then the shortest route will be from the stool to $B$ and thence to the door. Obviously, the shortest distance from $A$ to the door is the straight line, and as the distance from the stool to any point of the river is the same as from $A$ to that point, the correctness of the solution will probably appeal to every reader without any acquaintance with geometry.

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References

Project Gutenberg

1. Dudeney, H. E.: "Amusements in Mathematics", The Authors' Club, 1917

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