1。Last month, 15 homes were sold in town X. The average sale price of the homes was 150000 and the median sales price was 130000. which of the following statements must be true?
1 at least one of the homes was sold for more than 165000.
2 at least one of the homes was sold for more than 130000 and less than 150000.
3 at least one of the homes was sold for less than 130000.

A 1 only
B 2 only
C 3 only
D 1 and 2
E 1 and 3

此题选A，请问思路？

2 A centain law firm consist of 4 senior partners and 6 junor partners. How many different groups of 3 partners can be formed in which at least one member of the group is a senior partner?(Two groups are considered different if at least one group member is different.)
A 48
B 100
C 120
D 288
E 600

此题选 B。我算的是C 41 * C 92 = 144。

3。On a certain sight-seeing tour, the ratio of the number of women to the number of children was 5 to 2. What was the number of men on the sight-seeing tour?
条件1 On the sight-seeing tour, the ration of the number of children to the number of men was 5 to 11.
条件2 The number of women on the sight-seeing tour was less than 30.
 答案是C。请问条件2less than 30也能算出结果吗？

4 In the xy-plane, what is the y-intercept of line L?
条件1  The slope of line L is 3 times its y-intercept.
条件2  The x-intercept of line L is -1/3.

此题选什么呢？

请高手请教！！！多谢。

1 为了满足条件至少要有一个是(150000-130000)+150000, 1对
2 可以所有的都等于130000和170000，或者等于150000不一定要大于小于

，2错
3 同2

2题
C(4,1)C(6,1)+C(4,2)C(6,1)+C(4,3)

3题
可以算出女人和男人比例25/22，女人少于30人，小于30的数出了25意外

不能算出男人是整数，男人只能为22

4  4题
设y=ax+b
x=-b/a=-1/3
s/y=a/b=3

cannot reach the answer, I choose E

第二题应该选B  C(3,10) - C(3,6) = 120 - 20 = 100

至少一个是senior，用所有可能的组合减去没有senior的组合。

也可以C(4,1)C(6,2)+C(4,2)C(6,1)+C(4,3) = 4*15 + 6*6 + 4 = 100

含一个senior的组合 +  含两个senior的组合 + 全都是senior的组合