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标题: 请各位大大Prep Math部份共6题...解救我这个数学白痴..please [打印本页]

作者: yuching730 时间: 2007-8-9 03:04
标题: 请各位大大Prep Math部份共6题...解救我这个数学白痴..please

urgent!Prep Math部份3题,

请各位大大帮忙解救我这个数学白痴..please…

PS:

1.Three grades of milk are 1%, 2%, and 3% fat by volume. If X gallons of the 1% grade, y gallons of the 2% grade, and z gallons of the 3% percent grade are mixed to give x + y + z gallons of a 1.5% grade. What is X in terms of y and Z?

y+3z
(y+z)/4
2y+3z
3y+z
3y+4.5z

Ans: A

+
X
Y
Z
4
E
f
1
7
2
-5
N
-4
M
10
5

In the addition table shown above, what is the value of m+n?

Ans:5

3.DS:

Lines n and p lie in the xy-plane. Is the slope of line n less than the slope of line p?

(1)Line n and p intersect at the point (5,1)

(2)The y-intercept of line n is greater than the y-intercept of line p.

Ans:C,搞不懂为何知道二个交点及n的y比p大就可知n\p斜率谁大??

4.DS

If M is a finite set of negative integers, is the total number of integers in M an odd number?

(1)The product of all the integers in M is odd

(2)The product of all the integers in M is negative

Ans: B

5. of the 4,800 voters who voted for or against Resolution K, 1,800 were Democrats and 3,000 were Republicans. What was the total number of female voters who voted for Resolution K?

(1)3/4 of the Democrats and 2/3 of the Republicans voted for Resolution K

(2)1/3 of the Democrats who voted for Resolution K and 1/2 of the Republicans who voted for Resolution K were females.

Ans:C,為何答案不是B,因為A僅知支持K總共人數,而B很明顯就可知道the total number of female voters who voted for K了啊???請大家幫忙解惑…..

6. How much time did it take a certain car to travel 400 kilometers?

(1) The car traveled the first 200 kilometers in 2.5hr

(2) If the car’s average speed had been 20 kilometers per hr greater than it was, it would have traveled the 400 kilometers in 1 hr less time than it did.

Ans:B

第一個僅知前200km take 2,5hr而後200km部份題目並未說成比例關係所以不充份

第二個我就搞不懂了????請大家幫忙……

[此贴子已经被作者于2007-8-9 3:08:48编辑过]

作者: sammy生米 时间: 2007-8-9 05:24
先查查置顶的【数学讨论链接汇总】费费，GWD/涛涛31，GMATprep，钱永强有没有你所提的问题la

作者: mixtec 时间: 2007-8-9 13:12
1 列算式

（x%＋2y％＋3z％）/(x+y+z) = 1.5%

2 m=4+z, n=y+e => m+n = 4+y+z+e= -5 +10 = 5

3 画图一看便知

4 A －3*-3以及－3×－3×－3都满足A，但不合题意
B，乘积为负，M中所有数为负，说明有奇数个，否则乘积为正

刚吃完饭，做DS容易消化不良，等会儿来做

作者: mixtec 时间: 2007-8-9 14:02
5 Democrats who voted for Resolution K

6 设以前速度为x，则 400/x － 400/(x+20) ＝ 1，求出x，得出时间

不晓得对不对

作者: pockyqueen 时间: 2007-8-9 14:23

樓上的解釋已經很完整了

至於這題DS

5. of the 4,800 voters who voted for or against Resolution K, 1,800 were Democrats and 3,000 were Republicans. What was the total number of female voters who voted for Resolution K?

(1)3/4 of the Democrats and 2/3 of the Republicans voted for Resolution K

(2)1/3 of the Democrats who voted for Resolution K and 1/2 of the Republicans who voted for Resolution K were females.

Ans:C,為何答案不是B,因為A僅知支持K總共人數,而B很明顯就可知道the total number of female voters who voted for K了啊???請大家幫忙解惑…..

total 4800 voters=> 1800 D and 3000 R

1. you can only know 1800*3/4=1350D and 3000*2/3=2000R voted for K

2. you know 1/3 of D voted for K and 1/2 R voted for K were females

Ans: C combine 1&2 you know 1/3 of 1350D and 1/2 of 2000R are females voters who voted for K

hope my explanation is helpful =)

[此贴子已经被作者于2007-8-9 14:26:01编辑过]

作者: yuching730 时间: 2007-8-11 16:58
謝謝各位大大的點醒,我現在才發現有Premath的匯總,

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