大家帮忙看几道概率/排列组合题，谢谢

overmatch

我对于排列组合和概率问题那可真是一头雾水啊，以前学的都忘记了。这几道题目不知道怎么解出来的，麻烦大家帮忙看看，谢谢。
A certain office supply store stocks 2 sizes of self-stick notepads, each in 4 colors:blue, green, yellow, or pink. The store packs the notepads in packages that contain either 3 notepads of the same size and the same color or 3 notepads of the same size and of 3 different colors. If the order in which the colors are packed is not considered, how many different packages of the types described above are possible?
16

If a coin has an equal probability of landing heads up or tails op each time it is flipped, what is the probability that the coin will land heads up exactly twicein 3 consecutive flips?
0.375

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?
2/9

A jar contains 16 marbles, of which 4 are red, 3 are blue, and the rest are yellow.  If 2 marbles are to be selected at random from the jar, one at a time without being replaced, what is the probability that the first marble selected will be red and the second marble selected will be blue?
1/20

现在做这题目一点也没以前高中的感觉了，TT

overmatch

要沉掉鸟~~赶快顶一个。。。。大家帮忙说一下思路就好~~~~

tkrayla

第一题 他说有两个size 四个color 不管color怎样 反正size都是相同的
如果color相同 有4种排列 每个颜色一种
如果color不同 就是4个里面不重复的选三个 即P43
然后 有两种size 乘2就可以得到答案了

tkrayla

第二道题
抛三次硬币中选两次是正面朝上的 P32=3
然后两次朝上 一次朝下的概率是0.5*0.5*0.5=0.125
乘起来就好了

tkrayla

比如 那个passenger先按1 2 3的顺序做车厢
那么 他的概率是 1/3*3*3=1/27
车厢1 2 3的排列次序有六种 3*2*1
还是乘起来就行了

tkrayla

按题目看 应该是不放回的抽取
第一次抽到红的概率 4/16 第二次抽到兰的概率是 3/15 (15是因为已经抽了一个出来了)
乘起来就得到1/20

tkrayla

证毕。。。。继续啃阅读。。。

overmatch

谢谢哈，我的数学太差啦