7.ABCDEF六个人坐一张桌子，问A和FB相邻,B和AC相邻,C和BD相邻,D和CE相邻,E和DF相邻,F和EA相邻的概率这题没思路啊排列组合太差了怎么办啊
P=2/（6-1）！=1/60
这个环形排列高考常做
满足条件的只有两种情况：
A A
F B B F
E C C E
D D
8. 2个立方体，每面都是一个数字，1-6，同时抛，问最上方的那一面数字之和是5或者9的概率多少？ 5=2+3=1+4，so the probability could be 1/6 * 1/6 *2*2=1/9, 同理 9=3,6=4,5，p=1/9,so the final answer shall be 2/9.
9.to make a food, one may use chocolate and peanut, the cost of 2 pounds chocolate and 3 pounds peanut to make such a food is 3.8 per pound, if the cost of chocolate is 2 more than (or less than) that of peanut, how much does peanut cost?
10.the volume of two sphere has a ratio of 64, then what is the ratio of its surface area?
RATION 只给了一个64，另一个没给， 估计思路就是球体体积4/3 pai d³, 求出R，然后再表面积公式4 PAI R平方 比一下作者: xiongbaobao 时间: 2010-5-26 20:31
11. in a room, the source of light is in the central of ceiling, the room has a width of 16, length of 12, a height of 10, then what is the greatest distance that a light beam could reach within the house? cube ,calculate the diagonal distance，对角线
不会作图，我算的是
12. in a survey of the number of goose, scientists harvest A （数字忘记了)个 eggs and select 2 eggs out of 90% nests have more than 5 eggs, and there are B nests that have 4 eggs. There are no other nests. So what is the total number of nests surveyed ?
13. X is a positive integer and the sum of all the units digit is 170 , Y is a integer, and X=10^20-Y, then what might be the value of Y?
