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标题: PP中的这几道题应该怎样做？ [打印本页]

作者: chailin1017 时间: 2009-4-22 12:56
标题: PP中的这几道题应该怎样做？

在做PP时不知道这种描述是什么意思，请大家指点
In the xy-coordinate plane, line l and line k intersect at the point (4,3). Is the product of their slopes negative?
(1) the product of the x-intercepts of line l and line k is positive
(2) the product of the y-intercepts of line l and line k is negative.

还有3个题，就是
If k is positive integer, what is the digit of the handred?
(1) the handreds digit of k+150 is 4
(2) the tens digit of k+25 is 7

If m is positive odd integer, 求 average of a certain set of the integers
(1) the integers in the set are consecutive multipels of 3
(2) the median of the set of integers is 3

最后一个是说两个水管注水的问题，单独cold- water leak 用C hours, hot-water leak uses H hours (the same container, respectively)，如果一起注水的话，用T小时。
其中有一个是 C/2 < T < h/2
这个是怎么推导出来的？

作者: chailin1017 时间: 2009-4-22 20:47

不知道该怎么理解！

自己先顶一下

作者: fff777 时间: 2009-4-24 22:56

第一个题，

问相交于1点的2条线的斜率是否的product是否为负。

条件分别为他们在X Y轴的截距的product. 直线上的两点的纵坐标的差值比上横坐标的差值。这就是直线的斜率。

所以知道x y 的截距分别为Y2/Y1 正 X2/X1负他们的斜率product 是y2y1/x2x1 肯定为负选C

作者: fff777 时间: 2009-4-24 23:05

From stmt (1), the number 'k' can be between 250 to 349 ,both inclusive, as the numbers in this range would yield the hundreds digit as 4. So, the hundreds digit could be 2 or 3. Insuffcient.

From stmt (2), the number 'k' can be between 245-254...
Okay, while explaining my answer , I have found the correct answer. I am still posting this question, so that the explanation might benefit others. The number 'k' can be 145-154 also etc. since there is no restriction on the hundreds digit. Insufficient.

Together, the number can be 250 - 254 or 345-349. So, insufficient.

So, my ans is (E)

其他几个替补知道你的原题。把原题直接搜google一般都可以搜到的。我也问了几个数学题都一个礼拜都没有人回答。准备别处问去了

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