求解(数学)

1123581321

首先谢谢各位的解答。
1）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
怎么解？
2)A set of numbers has the property that for any number t in the set, t + 2 is in the set.If –1 is in the set, which of the following must also be in the set?

I.-3 II.1 III.5


A.I only  B.II only  C.I and II only   D.II and III only  E.I, II, and III

-3为什么不在这组数里？


3）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. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

答案是D，（2）为什么是sufficient？

cozy0128

第一题，假设三辆车分别为A、B、C，这个人第一次先选择了一辆车，假设为A车，当他再次选择时，按题目要求，只能从B、C两辆车中选择一辆，这样一来，第二次选择的概率为2/3，然后最后一次选择必须是仅剩下的一辆，因而概率是1/3，所以答案应该是2/9

第二个题目的关键在于must be，由题意知-1为数列中的一个数，那么1和5都是必须存在的，而-3不是必须存在，可以没有，因此选D

第三个题目我当时做也没理解，求高人指点

maximeason

三分之一 乘以 三分之一 乘以三分之一  这是比如A车 连续三次都抽到的概率
然后 再乘以三 代表3辆车概率的合 所以是九分之一
我数学不好 请后来的大师指教 我认为这样想正确

maximeason

不好意思 第一题我看错了 同意楼上的说法