m******t
发帖数: 273 | 1 【 以下文字转载自 Quant 讨论区 】
发信人: myregmit (myregmit), 信区: Quant
标 题: 面试题, make decision for two closed envelopes
发信站: BBS 未名空间站 (Thu Oct 3 13:00:22 2013, 美东)
An interview question:
Given two closed same envelopes, one may have $20 or $10, another one may
have $20 or $5.
You pick up one randomly and find it has $10, now you are given a chance to
make decision about whether to open another envelope.
If yes, you have to accept the money in it no matter it is more or less than
your $10 currently in your hand.
How to make the decision ?
Any help would be appreciated.
Thanks ! |
w****e
发帖数: 23 | |
j*****3
发帖数: 106 | 3 感觉这题不是在考概率啊，应该是考strategy或者personality的，反正要是我肯定拆
，同等概率下，收益大于损失啊 |
S******6
发帖数: 55 | 4 选择放弃$10,
这样选择到$5,只是损失了$5;若选择了$20就多了$10。何况损失5，跟多10的概率相同。 |
i*********7
发帖数: 348 | |
m****9
发帖数: 492 | 6 So the 2nd envelope has either 20 or 5. The expected value for the
2nd envelope: 20*.5+5*.5 = 12.5$.
You are thinking about risking 10$ to earn 12.5$. not opening the 2nd one
you earn 0, open the 2nd one you earn 2.5$. Definitely open the 2nd
one. |
g*********e
发帖数: 14401 | 7 条件不足啊
是不是要做题的自己假设信封中20或5的概率,然后算期望?
题目有点2 |
m******t
发帖数: 273 | 8 Why "open the 2nd one you earn 2.5$." ?
How to get 2.5$ ?
Thanks !
【在 m****9 的大作中提到】
: So the 2nd envelope has either 20 or 5. The expected value for the
: 2nd envelope: 20*.5+5*.5 = 12.5$.
: You are thinking about risking 10$ to earn 12.5$. not opening the 2nd one
: you earn 0, open the 2nd one you earn 2.5$. Definitely open the 2nd
: one.
|
m****9
发帖数: 492 | 9 You are "expected" to earn 12.5$-10$ = 2.5$. Each time you choose the 2nd
envelope may earn 5$-10$ = -5$, or you may earn 20$-10$ = 10$. These happen
50/50. But if someone offers such choices multiple times, always choosing
the 2nd envelope will be a good deal, right?
【在 m******t 的大作中提到】
: Why "open the 2nd one you earn 2.5$." ?
: How to get 2.5$ ?
: Thanks !
|
f*******w
发帖数: 1243 | |
j*****3
发帖数: 106 | 11 题目说了，就是简单的让人无法相信
【在 f*******w 的大作中提到】
: 题目也没有说是等概率啊。
: 感觉条件不足。
|
m******t
发帖数: 273 | 12 It looks simple.
I try to find out what the interviewer expects to know about the interviewee
from this question.
Any help would be appreciated !
【在 j*****3 的大作中提到】
: 题目说了，就是简单的让人无法相信
|
