求教两题

frankman

A certain roller coaster has 3 cars, and a passenger is equally likely to ride in any 1 of the 3 cars each time that passenger rides the roller coaster.  If a certain passenger is to ride the roller coaster 3 times, what is the probability that the passenger will ride in each of the 3 cars?

 

A.      0

B.       1/9

C.       2/9

D.      1/3

E.       1

A photographer will arrange 6 people of 6 different heights for photograph by placing them in two rows of three so that each person in the first row is standing in front of someone in the second row.  The heights of the people within each row must increase from left to right, and each person in the second row must be taller than the person standing in front of him or her.  How many such arrangements of the 6 people are possible?

 

A.    5

B.     6

C.     9

D.    24

E.     36

谢谢NN的指点了，自己很苦闷！

linjingsanxi

不是NN,这几天快要考了，刚好路过，进来看看，互相切磋吧~

第一题我选C.2/9。解题思路是这样的：要想ride in each of the three cars可能的情况就是每次坐到一个，三个车排列共P3(3)种，总的可能情况是3*3*3种，所以概率=P3(3)/(3*3*3)=2/9

第二题我没想到好方法，就老老实实把可能的情况列了一下：把六个人身高分别用1-6六个数字表示，则可能的情况有123-456、124-356、125-346、134-256、135-246这五种，所以选A。

 

如果觉得不对请指正哈~~

[此贴子已经被作者于2009-6-18 21:50:17编辑过]

frankman

应该对的，谢谢楼上的回答！