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借地问个概率题目

借地问个概率题目# WaterWorld - 未名水世界

x*g2013-09-20 07:09

1 楼

菜鸟没学过概率，更没有学过conditional probability,请牛人解答以下拉：
Marie is getting married tomorrow, at an outdoor ceremony in the desert. In
recent years, it has rained only 5 days each year. Unfortunately, the
weatherman has predicted rain for tomorrow. When it actually rains, the
weatherman correctly forecasts rain 90% of the time. When it doesn't rain,
he incorrectly forecasts rain 10% of the time. What is the probability that
it will rain on the day of Marie's wedding?

I*t2013-09-20 07:09

2 楼

P（下雨|预测）=P（预测|下雨）P（下雨）/（P（预测|下雨）P（下雨）+P（预测|天
晴）P（天晴））

x*g2013-09-20 07:09

3 楼

能不能稍微解释一下，看不太懂。。。多谢

【在 I*********t 的大作中提到】

: P（下雨|预测）=P（预测|下雨）P（下雨）/（P（预测|下雨）P（下雨）+P（预测|天
: 晴）P（天晴））

h*e2013-09-20 07:09

4 楼

This is a Bayes problem.
Long time didn't do math problems,
don't guarantee the accuracy, for reference only :)
R: rain F: forecast
P(R) = 5/365
P(F|R) = 0.9
P(^F|^R) = 0.1
P(F) = P(F|R)P(R) + P(F|^R)P(^R) = 0.9 * 5/365 + (1-0.1) * (1 - 5/365) = 0.9
P(R|F) = P(F|R)P(R)/P(F) = 0.9 * 5/365 / 0.9 = 5/365 = 1/73
So, the result is 1/73 .

In
that

【在 x*****g 的大作中提到】

: 菜鸟没学过概率，更没有学过conditional probability,请牛人解答以下拉：
: Marie is getting married tomorrow, at an outdoor ceremony in the desert. In
: recent years, it has rained only 5 days each year. Unfortunately, the
: weatherman has predicted rain for tomorrow. When it actually rains, the
: weatherman correctly forecasts rain 90% of the time. When it doesn't rain,
: he incorrectly forecasts rain 10% of the time. What is the probability that
: it will rain on the day of Marie's wedding?

c*02013-09-20 07:09

5 楼

楼上错了。。。

c*02013-09-20 07:09

6 楼

貌似应该酱紫，当然我也不保证正确。。。
字太丑了，瀑布汗-_- !

.9

【在 h****e 的大作中提到】

: This is a Bayes problem.
: Long time didn't do math problems,
: don't guarantee the accuracy, for reference only :)
: R: rain F: forecast
: P(R) = 5/365
: P(F|R) = 0.9
: P(^F|^R) = 0.1
: P(F) = P(F|R)P(R) + P(F|^R)P(^R) = 0.9 * 5/365 + (1-0.1) * (1 - 5/365) = 0.9
: P(R|F) = P(F|R)P(R)/P(F) = 0.9 * 5/365 / 0.9 = 5/365 = 1/73
: So, the result is 1/73 .

e*s2013-09-20 07:09

7 楼

楼上对了

x*g2013-09-20 07:09

8 楼

太感谢了。赞！

【在 c*0 的大作中提到】

: 貌似应该酱紫，当然我也不保证正确。。。
: 字太丑了，瀑布汗-_- !
:
: .9

h*e2013-09-20 07:09

9 楼

我跟你的分歧只在于对这句话的理解：
When it doesn't rain, he incorrectly forecasts rain 10% of the time.
你是 P(B|^A) = 0.1,
而我的是P(^F|^R) = 0.1,也就相当于 P(^B|^A) = 0.1
我把那个incorrectly当作否定了，
仔细想想，应该你的理解是对的。
语言不通害死人啊，哈哈。。。

【在 c*0 的大作中提到】

: 貌似应该酱紫，当然我也不保证正确。。。
: 字太丑了，瀑布汗-_- !
:
: .9

c*02013-09-20 07:09

10 楼

8客气o(∩_∩)o

【在 x*****g 的大作中提到】

: 太感谢了。赞！

c*02013-09-20 07:09

11 楼

^_^

【在 h****e 的大作中提到】

: 我跟你的分歧只在于对这句话的理解：
: When it doesn't rain, he incorrectly forecasts rain 10% of the time.
: 你是 P(B|^A) = 0.1,
: 而我的是P(^F|^R) = 0.1,也就相当于 P(^B|^A) = 0.1
: 我把那个incorrectly当作否定了，
: 仔细想想，应该你的理解是对的。
: 语言不通害死人啊，哈哈。。。

O*o2013-09-20 07:09

12 楼

niu.
saved the handwritting for furture reference
when I read the title, I was thinking I remembered a familar ID has said she
/he was very good at Proba. it was you.
BTW you do this a lot in the desert?

【在 c*0 的大作中提到】

: 貌似应该酱紫，当然我也不保证正确。。。
: 字太丑了，瀑布汗-_- !
:
: .9