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。
Tommy Smart was recently sent to a new school. On the first day of his arrival the teacher asked him his age, and this was his curious reply: "Well, you see, it is like this. At the time I was born—I forget the year—my only sister, Ann, happened to be just one-quarter the age of mother, and she is now one-third the age of father." "That's all very well," said the teacher, "but what I want is not the age of your sister Ann, but your own age." "I was just coming to that," Tommy answered; "I am just a quarter of mother's present age, and in four years' time I shall be a quarter the age of father. Isn't that funny?" This was all the information that the teacher could get out of Tommy Smart. Could you have told, from these facts, what was his precise age? It is certainly a little puzzling.
汤米·斯马特最近被送到一所新学校。到达的第一天，老师问他的年龄，他好奇地回答：“嗯，你看，是这样的。我出生的时候——我忘了是哪一年——我唯一的妹妹安，恰好只有母亲年龄的四分之一，现在她是父亲年龄的三分之一。” “那很好，”老师说，“但是我想要的不是你安姐姐的年龄，而是你自己的年龄。” “我正要说这个，”汤米回答道。 “我只有母亲现在年龄的四分之一，四年后我将是父亲年龄的四分之一。这不是很有趣吗？”这就是老师能从汤米·斯马特那里得到的全部信息了。根据这些事实，你能知道他的确切年龄是多少吗？这确实有点令人费解。
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 18 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。