伊凡和艾格在飞机上相遇。
“如果我没记错的话，你有3个儿子。”伊凡说，“他们现在多大了？”
“他们年龄的乘积是36，”艾格说，“他们年龄的和恰是今天的日期。”
“对不起，艾格，”一分钟后，伊凡开口道，“你并没有告诉我你儿子的年龄。”
“哦，忘记告诉你了，我的小儿子是红头发的。”
“啊，那就很清楚了，”伊凡说， “我现在知道你的3个儿子各是多大了。”
伊凡是怎么知道他们的年龄的？

there must be at least 2 sets of solution that can simultaneously satisfy the product/sum condition, but the fact that he has only 1 youngest son (if that's the implication...) removes that ambiguity, so the discarded solution must have the smaller 2 ages identical.

now 36 = 2x2x9 = 1x6x6, so 1,6,6 can be the answer