PREP 求解？

麦兜woo · 发表于 2010-10-6 02:55:48

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

A. 100%percent decrease
B. 50%decrease
C.40%decrease
D. 40%increase
E. 50%increase

答案选D，谁能帮忙解释下这道题什么意思，怎么做，题目都看不懂，越详细越好，O(∩_∩)O谢谢

语法：
The Achaemenid empire of Persin reached the Indus Vally in the fifth century BC, bringing the Aramdic script with it, from which was derived both northern and southern India alphabets.

A. the Aramdic script with it, from which was derived both nothern and
b. the Aramdic script with it, and from which was derived both nothern and the
C. with it the Aramdic script, from which derive both the northern and the
D. with it the Aramdic script, from which derives both northern and
E. with it the Aramdic script, and deriving from it both the northern and

答案选C，怎么来的？

chinamerica · 发表于 2010-10-6 03:31:35

一种化学反应速率与 A的浓度的平方成正比，与B的浓度成反比。
如果B的浓度增加100％，问A的浓度要增加多少才能使化学反应速率维持不变。

设化学反应速率为r，A的浓度为a, B的浓度为b.
则 r= k a^2 /b, where k 是常数
B的浓度增加100％，i.e., b-> 2b
如果r维持不变的话，a^2 需要变到2a^2,i.e, a需要变到 {\sqrt 2}a, 差不多1.414a, 也就是说a需要增长41.4%左右。

The Achaemenid empire of Persin reached the Indus Vally in the fifth century BC, bringing the Aramdic script with it, from which was derived both northern and southern India alphabets.

先看逻辑意思主要看从句到底是修饰什么.. 从句中 both northern and southern India alphabets derive from sth...
sth 应该是the Aramdic script. 注意到从句是倒装结构哈
A. the Aramdic script with it, from which was derived both nothern and 从句指代错误
b. the Aramdic script with it, and from which was derived both nothern and the 从句指代错误
C. with it the Aramdic script, from which derive both the northern and the 正确
D. with it the Aramdic script, from which derives both northern and ‘both northern and southern India alphabets’ 应该用复数动词derive
E. with it the Aramdic script, and deriving from it both the northern and 这里deriving from it....与前面的bringing.....平行，但显然这里bringing 和 deriving 的主语不可能都是'empire'

PREP 求解？

所属分类: GMAT考试

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