[讨论]PREP数学题目的综合讨论帖

sinowen

以下是引用冰岛哲学C在2007-12-15 11:47:00的发言：

就是高中时讲交集的时候老师老用的那个图~

..

题目就是求黄色+绿色的部分总和.  绿色为250..

不会用软件..画得好丑..LZ就凑伙着看吧~~呵呵。.

别告诉我是现场画的，感动中。。。

sinowen

63.   5266-!-item-!-187;#058&004544

The cost of delivery for an order of desk chairs was $10.00 for the first chair, and $1.00 for each additional chair in the order.  If an office manager placed an order for n desk chairs, is n > 24 ?

 

(1)  The delivery cost for the order totaled more than $30.00.

 

(2)  The average (arithmetic mean) delivery cost per chair of the n chairs was $1.36.

答案是B，我选择E。其实这里我更想明白一个看起来可能很简单的道理：就是如果DS题目当中问的是一般疑问句，比如本题；我用1和2的条件能够得到这个问句的答案，但是答案是否定的，那么答案是选择ABCD，还是E呢？按理来说，这不该是一个考过一次的人应该问的问题，但是。。。惭愧中。。。

sinowen

64.   5320-!-item-!-187;#058&004563

Are at least 10 percent of the people in Country X who are 65 years old or older employed?

 

(1) In Country X, 11.3 percent of the population is 65 years old or older.

 

(2) In Country X, of the population 65 years old or older, 20 percent of the men and 10 percent of the women are employed.

答案是B，但是我认为E。因为2中并没有提供对应的MEN和WOMEN所占比例呀。。。

冰岛哲学C

以下是引用sinowen在2007-12-15 11:56:00的发言：

别告诉我是现场画的，感动中。。。

这不是必然嘛..

呵呵...大家一起加油啦~~我19号就上阵了..比较壮烈。.没几天呢~

冰岛哲学C

以下是引用sinowen在2007-12-15 11:45:00的发言：

50.   4230-!-item-!-187;#058&003784

A construction company was paid a total of $500,000 for a construction project.  The company's only costs for the project were for labor and materials.  Was the company's profit for the project greater than $150,000 ?

 

 

(1)  The company's total cost was three times its cost for materials.

 

 

(2)  The company's profit was greater than its cost for labor.

答案选择C，我选择E。 我真是觉得里面的条件不足以得到PROFIT和数字之间的关系。。。

由条件(1)有 MATERIALS的费用为500,000/3. 

又 The company's only costs for the project were for labor and materials. 

则LABOR的费用为500,000*2/3

因为(2) The company's profit was greater than its cost for labor

所以profit> 500,000*2/3 > $150,000

sinowen

65.   5374-!-item-!-187;#058&004565

If x is a positive number less than 10, is z greater than the average (arithmetic mean) of x and 10 ?

 

(1) On the number line, z is closer to 10 than it is to x.

 

(2) z = 5x

答案是A，我选择B。举例，如果X=6, Z=7，那么Z比2/6+10小，所以题目的结论是错的。

其实又是回到我63题的疑问，还望NN解析。

冰岛哲学C

以下是引用sinowen在2007-12-15 11:53:00的发言：

56.   4741-!-item-!-187;#058&004206

During a sale, a clothing store sold each shirt at a price of $15 and each sweater at a price of $25.  Did the store sell more sweaters than shirts during the sale?

 

 

(1)  The average (arithmetic mean) of the prices of all of the shirts and sweaters that the store sold during the sale was $21.

 

 

(2)  The total of the prices of all of the shirts and sweaters that the store sold during the sale was $420.

答案是A，我选择B。我认为由于15和25的特殊性，而且没有小数点，那么这两个数在总和是420的前提下应该是一个绝对平衡的关系；的确是没有细算，但是如果A成立，B没有理由不成立呀。（说出来都觉得有点主观。。。）

由条件一有：　（１５Ｘ＋２５Ｙ）／（Ｘ＋Ｙ）＝２１

化简得：４Ｙ＝６／Ｘ　　　＝＞　　Ｙ／Ｘ＝６／４　　　又因为X.Y均为正数.

所以Y>X

条件二只能得出: 15X+25Y=420

不能进一步推出X.Y大小关系~

sinowen

79.   6946-!-item-!-187;#058&005390

If the terms of a sequence are t₁, t₂, t₃, . . . , t_n, what is the value of n ?

 

(1)  The sum of the n terms is 3,124.

 

(2)  The average (arithmetic mean) of the n terms is 4.

答案是C，我有是乱选个E。碰到这种题目真是没有花头了。。。

sinowen

84.   7517-!-item-!-187;#058&005572

If p is a prime number greater than 2, what is the value of p ?

 

(1)   There are a total of 100 prime numbers between 1 and p + 1.

 

(2)   There are a total of p prime numbers between 1 and 3,912.

答案是D，我选择还是乱来的E。题目的设计我觉得和79有些类似。但还是摸不着头脑。

冰岛哲学C

以下是引用sinowen在2007-12-15 13:33:00的发言：

65.   5374-!-item-!-187;#058&004565

If x is a positive number less than 10, is z greater than the average (arithmetic mean) of x and 10 ?

 

 

(1) On the number line, z is closer to 10 than it is to x.

 

 

(2) z = 5x

答案是A，我选择B。举例，如果X=6, Z=7，那么Z比2/6+10小，所以题目的结论是错的。

其实又是回到我63题的疑问，还望NN解析。

首先看题目.得:我们可以画出数轴           0-----------X-------------(X+10)/2--------------10

那么无论X在哪. the average (arithmetic mean) of x and 10 的点都会在X和10距离的中点.

也就是说图示中黄色的两段是相等的.

那么(1)说 z is closer to 10 than it is to x.  也就是说.Z落在右边的那段黄线中

那么Z是必然大于它左边的(X+10)/2 的..也就是 z greater than the average (arithmetic mean) of x and 10

把条件2代入已知题目中的条件: 则有5X>(X+10)/2

简化得:9X>10

X>10/9

而X只说是0到10中的正数..它可能比10/9大..也可能比10/9小

是推不出X>10/9的。也就推不出5X>(X+10)/2