74. Baxter's Dog. Here is an interesting puzzle, complementing the previous one. Anderson left the hotel in San Remo at 9 o'clock and was on the road for a whole hour when Baxter set out after him along the same route. Baxter's dog ran out at the same time as its owner and kept running back and forth between him and Anderson until Baxter caught up with Anderson. Anderson's speed is 2 km/h, Baxter's is 4 km/h, and the dog's is 10 km/h. How many kilometers did the dog run by the time Baxter caught up with Anderson?

The reader who sent me this problem, being a meticulous person, deemed it necessary to specify that "the length of the dog and the time spent turning can be neglected." I would add, on my part, that the dog's name and the day of the week can equally be neglected.
74. It is quite obvious that Baxter will catch up with Anderson in one hour, by which time they will have each traveled 4 km in the same direction. Furthermore, the dog’s speed is 10 km/h; therefore, in this hour, it will have run 10 km! When this puzzle was presented to a French mathematics professor, he exclaimed, “Mon Dieu, quelle série!”*, completely failing to notice how simple it was to solve.