求救~~数学题目

九天仙女 · 发表于 2009-12-3 22:02:09

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

keaneice · 发表于 2009-12-3 22:14:18

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

x是和，用等差数列求和公式求和
Y是个数，用等差数列求个数公式，[（末项-首项）/公差 ] + 1

keaneice · 发表于 2009-12-3 22:17:59

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

A. 2 B. 3 C.5 D.7 E.11

化简=2^34-2^28=(2^6-1)*2^28
所以求(2^6-1)的质因子就行了 =63，最大7

keaneice · 发表于 2009-12-3 22:23:38

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

11-2月共生产 4x ，3-10月每月运走x/2，3-10月每R付0.1元，所以从三月开始就 3.5，3，2.5，2，1.5，1，0.5，的等差数列，求和，乘以0.1=1.4x

feymaggie · 发表于 2009-12-3 22:26:12

4¹⁷-2²⁸

^{= 2 ^34 - 2^28}

^{=2^28(2^6-1)}

^{=2^28*63}

^63=7*9

keaneice · 发表于 2009-12-3 22:30:02

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 · 发表于 2009-12-3 22:31:21

数学真好呵呵这次的JJ多亏你的详解版谢谢

keaneice · 发表于 2009-12-3 22:32:52

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

keaneice · 发表于 2009-12-3 22:33:53

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

九天仙女 · 发表于 2009-12-3 23:38:55

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。

求救~~数学题目

第二题是不是选D=7 我数学也不好下面是我的解法

谢谢KEANENECE

所属分类: GMAT考试

正在浏览此版块的会员 ()

求救~~数学题目

第二题是不是选D=7 我数学也不好 下面是我的解法

谢谢KEANENECE

所属分类: GMAT考试

正在浏览此版块的会员 ()

第二题是不是选D=7 我数学也不好下面是我的解法