马上要考试了 PREP6道数学错题求教

apply408 · 发表于 2007-11-13 22:18:00

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.

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

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.

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.

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

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?

我的数学真寒~要麻烦各位NN帮忙解答了~谢谢了

[此贴子已经被作者于2007-11-13 22:21:29编辑过]

apply408 · 发表于 2007-11-14 08:55:00

期待回复~

crazecat123 · 发表于 2007-11-14 15:17:00

以下是引用apply408在2007-11-13 22:18:00的发言：

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

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?

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

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?

65. (C) Two (2 and 4)

116. 选sibling一共只有60种组合，但一共有1000*800种配对儿。所以概率是　60/800000

ludi19842004 · 发表于 2007-11-14 17:11:00

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.

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

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.

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.

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

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?

我的数学真寒~要麻烦各位NN帮忙解答了~谢谢了

64.条件一没用;条件二行,既然男的和女的都超过或等于10%,总数一定大于10%

65.两个条件都不行举两个反例吧　（１）　Ｘ＝２，Ｚ＝３　２＋１０／２＞３　（２）Ｘ＝１，则Ｚ＝５　１＋１０／２＞５

sea_fairy · 发表于 2007-11-14 19:25:00

以下是引用ludi19842004在2007-11-14 17:11:00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.

64.条件一没用;条件二行,既然男的和女的都超过或等于10%,总数一定大于10%

条件2是of the population 65 years old or older, 20 percent of the men and 10 percent of the women are employed.意思是65 years old or older中有20 percent of the men and 10 percent of the women are employed！

所以：一共有X人。 11.3%*X*30%/X=11.3%*30%=3.39% 小于10% 应该选C。

C E E C C 3/40000

红白蓝小球那个不确定。。。

wsgyj · 发表于 2007-11-14 22:11:00

64题俺觉得应该选B，设〉=65岁中employed的男人数为M，女人数为F

有（0.2M+0.1F）/（M+F）为employed 的人显然大于10%所以选B

65题俺觉得应该选A，因为Z比X更靠近10，所以Z〉（X+10）/2

ludi19842004 · 发表于 2007-11-15 01:59:00

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.

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.

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

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?

继续

158. 条件一不行只能说明没有上面带偶数的红球

条件二也不行只能说明红球比偶数球多25*0.2,即5个

但是两个条件联立就可以了,在第一个条件下, 红球的个数最多只能有5个,也就是说抽中红球的概率是5/25,即0.2

又又条件二抽红球减抽偶球概率为0.2,得出抽中偶球概率为0,

所以抽中红球或偶球的概率为0.2+0=0.2

204.条件一说明 C/M=5/11 不能得出人数

条件二单独也不能得出什么

但是两个条件联立加上题目已知条件可以求解

现在有 C/W=2/5, C/M=5/11, 那么W=25/22M, M只能是22的倍数,又有M<30, 所以M=22

sea_fairy · 发表于 2007-11-15 10:06:00

以下是引用wsgyj在2007-11-14 22:11:00的发言：

64题俺觉得应该选B，设〉=65岁中employed的男人数为M，女人数为F

有（0.2M+0.1F）/（M+F）为employed 的人显然大于10%所以选B

65题俺觉得应该选A，因为Z比X更靠近10，所以Z〉（X+10）/2

64应该选B阿。。。我看错题了。。。。

笨死了。。。

apply408 · 发表于 2007-11-15 14:27:00

太感谢crazecat123，ludi19842004，sea_fairy，wsgyj。

红白兰球这题PREP给的答案是E，还是不明白，麻烦NN解释一下~

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.

sea_fairy · 发表于 2007-11-15 14:53:00

以下是引用apply408在2007-11-15 14:27:00的发言：

太感谢crazecat123，ludi19842004，sea_fairy，wsgyj。

红白兰球这题PREP给的答案是E，还是不明白，麻烦NN解释一下~

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.

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！！

马上要考试了 PREP6道数学错题求教

马上要考试了 PREP6道数学错题求教

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