马上要考试了 PREP6道数学错题求教

apply408

谢谢楼上，明白了

ludi19842004

 

题目 就是要求 P（WHITE）+ P（EVEN）=？

现在知道的是：条件1， 所有的 WHITE都标的奇数。  条件2， P（WHITE）- P（EVEN）=0.2

                        题目本身条件， 25个球，红白蓝色， 用1~10标号i

问题就变成    2P（WHITE）- 0.2=?        但是P（WHITE）是求不出来的！！

我认为可以求出来啊

条件1说明最多五个白球 P（W）《5/25=0.2

条件2 P(W)-P(E)=0.2 只有一种可能 P(W)=0.2(E)=0

那不就可以求出 P(W or E)=P(w)+P(E)=0.2

xunswift

以下是引用apply408在2007-11-13 22:18:00的发言：

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.

C。。。这个题标准答案似乎是B，很奇怪。。。

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

A。坐标轴上X和10的等分点就是算术平均之。条件二在10/9前后不同结论。

158. 15810-!-item-!-187;#058&010518

Each of the 25 balls in a certain box is either red, blue, or white and has a number from 1 to 10 painted on it.  If one ball is to be selected at random from the box, what is the probability that the ball selected will either be white or have an even number painted on it?

(1)  The probability that the ball will both be white and have an even number painted on it is 0.

(2)  The probability that the ball will be white minus the probability that the ball will have an even number painted on it is 0.2.

E。怎么说呢，我也忘了概率的那些术语怎么说，我的诀窍就是，一维（只有一个性质不同的的裙体）的就要知道2个量，二维的就要知道3个量。但这不包括不同衡量标准的量，一般而言，有数量和比率两种衡量标准。如果要在数量和比率之间搭桥，那就还需要在这两种量中至少知道一个。

。。。。这段话大概也就我自己能看懂

204. 19682-!-item-!-187;#058&012407

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?

(1)  On the sight-seeing tour, the ratio of the number of children to the number of men was 5 to 11.(2)  The number of women on the sight-seeing tour was less than 30.

C，第一个给比例，第二个给数字（小孩的个数是5X，所以女人的个数是25y）

65.   7870-!-item-!-187;#058&005675

For how many integers n is 2^n = n^2 ?

(A) None

(B) One

(C) Two

(D) Three

(E) More than three

3个。画图，有3个交点，第一象限2个（因为y=2^x比y=x^2升得快），第二象限1个

-，-看错了，整数阿。。。二象限那个显然不是整的。。。

116. 11659-!-item-!-187;#058&007807

A certain junior class has 1,000 students and a certain senior class has 800 students.  Among these students, there are 60 sibling pairs, each consisting of 1 junior and 1 senior.  If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair?

[（60/1000）*（1/800）+（60/800）*（1/1000）]/2=60/80000。。。这样好像挺绕的。。。不过比较直观。。。

[此贴子已经被作者于2007-11-15 19:13:06编辑过]

atc

 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.

解：这道题目没做对主要是没有理解题目意思：问65岁（含）中employed是否at least10%？

1）65岁（含）为11.3%，没用

2）65岁（含）employed：男为20%，女为10%。不管男女比例，至少为10%。选B

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

解：1）联系平均值概念和中点概念，成立

      2）判断(x+10)/2与z=5x关系（x〈10），不能确定。选A

158. 15810-!-item-!-187;#058&010518

Each of the 25 balls in a certain box is either red, blue, or white and has a number from 1 to 10 painted on it.  If one ball is to be selected at random from the box, what is the probability that the ball selected will either be white or have an even number painted on it?

(1)  The probability that the ball will both be white and have an even number painted on it is 0.

(2)  The probability that the ball will be white minus the probability that the ball will have an even number painted on it is 0.2.

解：1）告诉white的标号只能为奇数

      2）P（W）-P（E）=0.2

结合1），·2）将分类：W奇，（R，B）奇，（R，B）偶，有P（W奇）-P（（R，B）偶）=0.2。加上P（W奇）+P（（R，B）偶）+P（（R，B）奇数=1，求不出P（W奇）+P（（R，B）偶）=？ 选E

204. 19682-!-item-!-181）7;#058&012407

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?

(1)  On the sight-seeing tour, the ratio of the number of children to the number of men was 5 to 11.(2)  The number of women on the sight-seeing tour was less than 30.

解：1）得出W：C：M=25：10：22

      2）没用

结合1）2），M=22 选C

65.   7870-!-item-!-187;#058&005675

For how many integers n is 2^n = n^2 ?

(A) None

(B) One

(C) Two

(D) Three

(E) More than three

解：画图有3个解，但有一个是负数非整数解，选C。

116. 11659-!-item-!-187;#058&007807

A certain junior class has 1,000 students and a certain senior class has 800 students.  Among these students, there are 60 sibling pairs, each consisting of 1 junior and 1 senior.  If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a sibling pair?

解：事件总数：1000×800，条件事件60，概率60/（1000×800）