题面摘自 Henry E. Dudeney 公版文本；英文为古腾堡原文整理，中文为本站自译，提示、解答骨架和闲谈保留本站原创结构。
During a visit to the seaside Tommy and Evangeline insisted on having a donkey race over the mile course on the sands. Mr. Dobson and some of his friends whom he had met on the beach acted as judges, but, as the donkeys were familiar acquaintances and declined to part company the whole way, a dead heat was unavoidable. However, the judges, being stationed at different points on the course, which was marked off in quarter-miles, noted the following results:—The first three-quarters were run in six and three-quarter minutes, the first half-mile took the same time as the second half, and the third quarter was run in exactly the same time as the last quarter. From these results Mr. Dobson amused himself in discovering just how long it took those two donkeys to run the whole mile. Can you give the answer?
在访问海边期间，汤米和伊万杰琳坚持要在沙滩上进行一英里赛跑的驴赛跑。多布森先生和他在海滩上遇到的一些朋友担任评委，但是，由于驴子是熟人，一路上都不肯分手，所以一场争执是不可避免的。然而，在以四分之一英里为单位的赛道上，驻扎在不同地点的裁判员注意到了以下结果：前三节跑的时间为六又四分之三分钟，前半英里的时间与后半英里的时间相同，第三节的跑时间与最后一节的时间完全相同。从这些结果中，多布森先生发现这两头驴跑完一英里需要多长时间，这让他感到很有趣。你能给出答案吗？
提示 1
先说出现象：哪些量会变，哪些约束不会变。
提示 2
找守恒量、相似关系、平衡条件或不变量，不急着代公式。
提示 3
把物理图景或谜题结构翻成一个最小方程组，再处理边界情况。
完整解答
解题主线是先把 Dudeney 谜题 43 的条件整理成一个稳定模型，再选择最少的变量。第一步确认约束，第二步写出关键关系，第三步检查特殊情形。这里给的是原创解法骨架；若要核对原始题面，请回到公版来源。
这类题最怕一上来套公式。先把图景或语言条件说清楚，答案通常会少绕很多路。