标题: prep 数学 请教 [打印本页] 作者: hehejack 时间: 2010-7-26 16:24 标题: prep 数学 请教 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？作者: maggie520 时间: 2010-7-26 16:28
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%作者: wenjie87 时间: 2010-7-26 16:36
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作者: hehejack 时间: 2010-7-26 20:04
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。