prep 数学请教

hehejack · 发表于 2010-7-26 16:24:01

请教各位nn一道prep数学题;
Each employee on a certain task is either a mananger or a director, what percentage of employee on the task are managers?
(1) Tha average (arithmetic mean ) salary of the managers on the task is $5000 less than the average of all employee of the task
(2) Tha average (arithmetic mean ) salary of the directors on the task is $15000 greater than the average of all employee of the task

答案是C，两个一起就是sufficient，单独一个不是

百思不解，average和人数的关系是什么？还有，each manager或者each director的工资相等吗？

maggie520 · 发表于 2010-7-26 16:28:54

employee on a certain task is either a mananger or a director 这句话告诉你这个员工不是manager就是director,因此要percentage的话就需要2种职位的工资. 所以光知道1)或者2)是不够的。
director= 15000+avg
manager=avg-5000
you want to know manager/(manager+director) x100%

wenjie87 · 发表于 2010-7-26 16:36:08

设总人数为n, manager占总人数的比例为x, average salary of all employee为k
那么，两个条件合起来就可以得到表达式 n*x(k-5000)+n*(1-x)(k+15000)=n*k
化简约分出来就可得到 x=3/4

hehejack · 发表于 2010-7-26 20:04:10

懂了，谢谢啊。但是还是有个隐含的前提是每个M或者每个D的salary是相同的。

prep 数学请教

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prep 数学 请教

所属分类: GMAT考试

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prep 数学请教