请教大家2个数学题。多谢

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[attachimg]49370[/attachimg]

这是我从Gmat Prep上找的，我看不大明白，哪位能帮我翻译一下，然后再解答一下？谢谢

please check my answer first:

1 two together, result is 25%

2 D 41.4%

我重新编辑了,你的图片看不清楚.

1. Each employee on a certain task force is either a manager or a director. What percent of the employees on the task force are directors?

1)The average (arithmetic mean) salary of the managers on the task force is $5,000 less than the average salary of all emplyees on the task force.

2)The average (arithmetic mean) salary of the directors on the task force is $15,000 greater than the average salary of all emplyees on the task force.

第一题应该是C,

解法:设几个未知数, A_d为Director的平均工资, A_m为Manager的平均工资, D为Director的人数,M为Manager的人数

从条件1可知: A_m+5000 = (A_m*M+A_d*D)/(M+D)   ===> D/(D+M)=5000/(A_d-A_m)

从条件2可知:A_d-15000 = (A_m*M+A_d*D)/(M+D)   ===> M/(D+M)=15000/(A_d-A_m)

从两个条件综合可知: A_d-A_m=20000,  代入上两式,左边值可求得.

2. 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 increased by 100 percent, which of the following is closest to the percent change in the concentration of chemical A required to keep the reaction rate unchanged?

A. 100% decrease

B. 50% decrease

C. 40% decrease

D. 40% increase

E. 50% increase

这题前人已经有帖子解答,题目说某反应速度与A浓度平方成正比,与B浓度成反比,可以理解成

V=k * A² / B, (k为一个常数,只为完整性,不需考虑) 现假设B增加1倍,问A如何改变可保持反应速度不变.

V=k * (根号2)² * A² / 2B 约等于 k * (1+41.4%)² * A² / 2B

应该选D

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http://forum.chasedream.com/dispbbs.asp?boardID=22&ID=176560&page=1