28日上战场, 还需些弹药准备,XDJM帮个忙!

USbaby

两天就要考了,不知那天天气如何,FL这边飓风多,希望是个好天气,祝将考试和将申请的CDERS成功!

以下有几道做PREP时遇到的问题,请大家帮忙看看:

1.  The rate of a certain chemical reaction is directly proportional to the square of the concentaration of chemical of A present and inversely proportional to the concentration ofo chemical B present. If the concentration of chemical B is increased by 100 percent, which of the following is closest to the percent change in the concentration of chemical A required to keep the raction rate unchanged?

Answer: 40% decrease.

看不懂是什么意思,怎么求解?

 

2.If each term in the sum a1+a2+.....+an is either 7 or 77 and the sum equals 350, which of the following would be equal to n?

Answer: 40.

 

如何得出的40 呢?

3.(SC). A study on couple's retirement transitions found that women who took new jobs after retiring from their primary careers reported high marital satisfaction, more than when retiring completely.

其他的选项知道错在哪, 画线是我选的, 正确答案是: more so than those who retired. (??)

USbaby

续, 上边的贴:

4. what is the average (arithmetic mean) height of the N people in a certain group?

(1)the average height of the (n/3) tallest people in the group is 6 feet 2.5inches, and the average height of the rest of the people in the group is 5 feet 10 inches.

(2) The sum of the heights of the N people is 178 feet 9 inches.

I chose D, answer is A.

5.A certain group of car dealerships agreed to donate x dollars to a Red Cross chapter for each car sold during a 30-day period. What was the total amount that was expected to be donated?

(1) A total of 500 cars were expected to be sold

(2) 60 more cars were sold than expected, so that the total amout donated was $28,000.

I chose D, the answer is C.

6. If *denotes one of two arithmetic operations, addition or multiplication, ans if k is an integer, what is the value of 3 * k?

(1) 2*k=3

(2) 1*0=k

I chose D, answer is A

3rdforce

偶还没开始看数学,但觉得第一题答案似乎应该是40 pct increase,要不就是题目有点问题,因为rate= A的平方/B,当B增加一倍时,要使得rate不变的话,A要增加至"根号2乘以A"才能使分子等于"2乘以A的平方",最后的结果还是等于"A的平方/B",所以A要增加41.4%,约等于40 pct increase.

第二题比较简单,根据题目,假设需要a个77和b个7,则77a+7b=350 -> 7(11a+b)=350 -> 11a+b=50 -> a+b=50-10a, 题目要求的就是sum就是a+b,所以这个sum等于50 or 40 or 30 or 20 or 10.

SC偶还没开始看, can't help

fannyyudan

Math:

1. A的浓度a％的平方与实验结果有关，而B的浓度b％与实验结果有关，所以a％^2=b％才能使实验结果不变，当b%变成两倍，a%就增加根号2就可以使两个平均了。不知道解释清楚了没

2.77a+7b=350-->7*11a+7*b=7*50-->11a+b=50,取值代入，a=1时b=39,a=2时b=28,a=3,a=4,不认为这里a可以等于0，但还好ETS没有给我们制造这种疑惑答案

4.用条件A,可以取到平均值，因为此条件不需要具体人数，average=[6 feet 2.5inches+2×（5 feet 10 inches）]/3,而条件B有了总身高，但没有总人数，求不出平均值

5.答案是问的expected,所以A只能得出500x，B能得出x=2800/(500+60),两个一起才能得出最后的数据

6.*代表加法或乘法，2*k=3，且k只能是整数，所以k等于1，而不能是1.5，而且那个符号是代表加法，这样3*k=4,而光有B，k值不知道，所以什么都不知道，这里不能用A得出来的结论用在B上

[此贴子已经被作者于2006-6-26 10:16:16编辑过]

fannyyudan

SC:

3.(SC). A study on couple's retirement transitions found that women who took new jobs after retiring from their primary careers reported high marital satisfaction, more than when retiring completely.

其他的选项知道错在哪, 画线是我选的, 正确答案是: more so than those who retired. (??)

说实话，我也是第一次在SC中见到比较级这样的用法，谢谢MM分享，搜索google可以找到无数个例子

We also find substantial age differences between same-sex partners, more so than in opposite-sex marriages

so应该是用来代替就近的宾语，做同位语（不确定），如果没有这个so，more than的逻辑主语就显得不明确，原句中的when retiring作为比较对象显然很awkward,不划线部分找不到对应的时间状语。

USbaby

非常感谢大家的解惑答疑, 加油!