M*****y
发帖数: 666 | 1 【 以下文字转载自 Quant 讨论区 】
发信人: MsPiggy (coconut), 信区: Quant
标 题: 一道关于两倍年龄的题目
发信站: BBS 未名空间站 (Thu Mar 11 19:32:14 2010, 美东)
有没有高手来说说这道题怎么讨论？
两个人，A,B. A的年龄比Ｂ大。
For what length of time in their lives will A's age be twice B's age? (此处
的年龄说的是 truncated integer age). 还有一个assumption是两个人都可以无限地
活下去。
假设不限定具体的年龄数，该如何讨论这道题目呢？多谢！
我自己觉得无论Ａ，Ｂ多少岁，这个问题的答案始终是１年
不知道对不对，有什么合理的讨论方法 |
l***8
发帖数: 149 | 2 Let set T = {t | 2 * floor(t) == floor(t + A.age - B.age)}
Let c = floor(A - B), d = (A - B) - c
Then T = {t | (t >= c && t < c + 1 - d) || (t >= c + 2 - d && t < c + 2)}.
Therefore the measure of T is 1. |
M*****y
发帖数: 666 | 3 Thanks!!!! That makes a lot of sense!
【在 l***8 的大作中提到】
: Let set T = {t | 2 * floor(t) == floor(t + A.age - B.age)}
: Let c = floor(A - B), d = (A - B) - c
: Then T = {t | (t >= c && t < c + 1 - d) || (t >= c + 2 - d && t < c + 2)}.
: Therefore the measure of T is 1.
|
f**r
发帖数: 865 | 4 what does it mean by "truncated integer age"? does that mean the age could
overflow? |
M*****y
发帖数: 666 | 5 it means if my age now is 27 and next month on my birthday, my age will
become 28
【在 f**r 的大作中提到】
: what does it mean by "truncated integer age"? does that mean the age could
: overflow?
|
