求!!!PREP数学DS一道

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.

答案是C

可是我算不出来啊...总觉得少了点什么

我设manager是X人 director是y人 总工资是Z 但是确定不了manager和director的各自工资总数是多少 谁来指点下吧...

偶想想......

按你想的往下做：根据条件一二可得，a=b-20000，a,b分别为M和D的平均工资。根据等式M总工资+D总工资=总体工资，有ax+by=(b-15000)*(x+y), 把上式代入得：bx-20000x+by=bx+by-15000x-15000y, 约了等于20000x=15000x+15000y, 所以有4x=3(x+y),x/x+y=3/4, 所以答案为1/4.

jarlin你看对吗？