求ＰＲＥＰ－ＤＳ－１－１４７思路

147.
                14800-!-item-!-187;#058&010134

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 employees 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 employees on the task force.

答案　Ｃ

怎么求的呢

我又白痴了

请高人指教

谢谢

设平均工资为x

 Manager x-5000  人数为 M

 Director x+15000  D

x*(M+D)=(x-5000)*M+(x+15000)*D

可以求出M/D ，从而得到答案