求救~~数学题目

九天仙女

求助：模考数学 这几个题 实在搞不清楚 希望大N 赐教

Problem Solving

1.       If X is equal to the sum of the even integers from 40 to 60, inclusive, and y is the number of even integers from 40 to 60, inclusive, what is the value of x+y?

A.      550  B. 551 C. 560 D.561 E.572

2.       What is the greatest prime factor of 4¹⁷-2²⁸?

A.      2 B. 3 C.5 D.7 E.11

3.       A certain business produced X ranks each month from November through February and shipped X/2 ranks at the beginning of each month from March through October. The business paid no storage costs for the rakes from November through February, but it paid storage costs of $0.1 per rake each month from March through October for the rakes that had not been shipped. In terms of X, what was the total storage cost, in dollars, that the business paid for the 12 months from November through October?

A.      0.4x    B. 1.2x   C. 1.4x    D. 1.60x    E. 3.2x



Data Sufficiency  

4.       The lifetime of all the batteries produced by a certain company in a year have a distribution that is symmetric about the mean m, if the distribution has a standard deviation of d, what percent of the distribution is greater than m+d ?

1)       68 percent of the distribution lies in the interval from m-d to m+d, inclusive

2)       16 percent of the distribution is less than m-d

5.       Are the integers z and f to the right of 0 on the number line?

1)       The product of z and f is positive

2)       The sum of z and f is positive

zzqqyy87517

4.       The lifetime of all the batteries produced by a certain company in a year have a distribution that is symmetric about the mean m, if the distribution has a standard deviation of d, what percent of the distribution is greater than m+d ?

1)       68 percent of the distribution lies in the interval from m-d to m+d, inclusive

2)       16 percent of the distribution is less than m-d

1）只知道中间的，不知道less的，不充分
2）只知道less的，不知道中间的，不能求greater
结合一二可求
C

-- by 会员 keaneice (2009/12/3 22:30:02)

小K童鞋  这道题 我做也是C 可是模考上给的答案是D.... 是答案错了还是有什么地方没有想到呢？

九天仙女

哦~原来题的意思是说 y 的值是 40 到60 的偶数的个数啊。。我还以为是40 到60 之间任意一个偶数呢~~

天呐~我真。。不知道该说什么好了。

anyway, 3x2u 3x2u

keaneice

啊啊啊啊~我只能说你太厉害了，怎么数学头脑这么好

多谢死你了~佩服，佩服。

PS：

1.等差数列还有求个公式？干什么的？就是算出等差数列里随便的一项？

第五题，product 原来是乘积的意思啊，我愣是没搞明白。

-- by 会员 九天仙女 (2009/12/3 23:38:55)

就是求一共数列里面有多少项 ：）

九天仙女

啊啊啊啊~我只能说你太厉害了，怎么数学头脑这么好

多谢死你了~佩服，佩服。

PS：

1.等差数列还有求个公式？干什么的？就是算出等差数列里随便的一项？

第五题，product 原来是乘积的意思啊，我愣是没搞明白。

keaneice

数学真好 呵呵 这次的JJ多亏你的详解版 谢谢

-- by 会员 feymaggie (2009/12/3 22:31:21)

你。。你。。过奖了，我也只是顺手帮忙整理了下

keaneice

5.       Are the integers z and f to the right of 0 on the number line?

1)       The product of z and f is positive

2)       The sum of z and f is positive

1）乘积为正，可能是2个正数，也可能是2个负数，不充分
2） 和为正，可能两个正，也可能一个正，一个负，不充分
结合1、2，1）说明同号，2）说明为正，所以在0右边， 选C

以上答案都不保证正确，有问题请feel free的质疑

feymaggie

数学真好 呵呵 这次的JJ多亏你的详解版 谢谢

keaneice

4.       The lifetime of all the batteries produced by a certain company in a year have a distribution that is symmetric about the mean m, if the distribution has a standard deviation of d, what percent of the distribution is greater than m+d ?

1)       68 percent of the distribution lies in the interval from m-d to m+d, inclusive

2)       16 percent of the distribution is less than m-d

1）只知道中间的，不知道less的，不充分
2）只知道less的，不知道中间的，不能求greater
结合一二可求
C

feymaggie

4¹⁷-2<sup>28  

= 2 ^34 - 2^28

=2^28(2^6-1)

=2^28*63

63=7*9</sup>