严重受挫！！涛涛 GWD-3-2;3;30 需要大家的帮助！

citicsbond · 发表于 2006-7-19 18:25:00

3-2; on Saturday morning, Malachi will begin a camping vacation and he will return home at the end of the first day on which it rains. if on the first three days of the vacation the probability of rain on each day is 0.2, what is the probability that Malachi will return home at the end of the day on following Monday?

a. 0.008 ; b. 0.128 ; c. 0.488 ; d. 0.512 ; e. 0.640

3-3; Each of the 45 boxes on shelf J weighs less than each of the 44 boxes on shelf K. what is the median weight of the 89 boxes on these shelves?

1. the heaviest box on shelf J weighs 15 pounds.

2. the lightest box on shelf K weiths 20 pounds.

3-30; the membership of a committee consists of 3 English teachers, 4 Mathematics teachers, and 2 Social Studies teachers. if 2 commitee members are to be selected at random to write the committee's report, what is the probability that the two members selected will both be English teachers?

Is there anybody could help me with the above questions?

kdjd · 发表于 2006-7-19 23:13:00

3-2 选B
下雨的概率p1＝0.2
不下雨的概率p2=0.8
他下周一回来说明周六周日不下雨，周一下雨。概率就是0.8*0.8*0.2=0.128

3-3 选A
89是奇数，所以这里的median指所有箱子按重量从小到大中间排列后最中间那个的重量，既第45个。
所有的J都比K的箱子轻，所以排到第45个肯定是J里面最重的。
1足够。

3-30
总人数是3+4+2=9
两个都是英语的是C(2,3)/C(2,9)＝1/12

我觉得是这么做的，不知道答案对不对？

silviaqiu · 发表于 2006-7-19 23:44:00

答案正确

citicsbond · 发表于 2006-7-20 17:02:00

thank u.

christlulu · 发表于 2006-10-31 15:25:00

终于找到讨论贴了。。。

seanw2008 · 发表于 2008-5-6 23:42:00

请教楼上各位，C(2,3)/C(2,9)是什么含义？

blogfish · 发表于 2008-5-9 00:58:00

C是组合combination的缩写，

C(2,3)代表从3个英语教师里面选2个的可能

C(2,9)代表从9个成员里面随机选两个的可能

C(2,3)/C(2,9)即所选2个成员里面都是英语教师的概率

希望解释清楚了：）

harry2006 · 发表于 2008-5-11 02:36:00

It's same as the way: 3/9 * 2/8 = 1/12

nerakuhs · 发表于 2009-1-16 17:18:00

thanks

jingle0915 · 发表于 2010-7-29 20:11:13

谢谢

严重受挫！！涛涛 GWD-3-2;3;30 需要大家的帮助！