please help! gwd1-2 math

Q2:

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

Answer:

我用列举法 很快就能发现答案 （方法很笨，但很实用，呵呵）

假设这三个车子分别是A、B、C，可以排列组合：

AAA AAB AAC ABA ABB ABC ACA ACB ACC (相信罗列到这里，你就知道答案了）

BAA BAB BAC BBA BBB BBC BCA BCB BCC

CAA CAB CAC CBA CBB CBC CCA CCB CCC

最后答案：2/9

用排列组合作的话就是P33/P31*P31*P31也可以得到2/9的答案~

thank you

正好遇上这道题想不通的

还有这道题,答案选D,不明白

我觉得应该选A或者C才是啊

Joanna bought only $0.15 stamps and $0.29 stamps.  How many $0.15 stamps did she buy?

(1)     She bought $4.40 worth of stamps.

(2)     She bought an equal number of $0.15 stamps and $0.29 stamps.

A is right.

In GWD, two answers are given, A ( n-1 times) and D ( 1 time).

刚刚算错了，A对，不是D

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