还是问PREP数学，已解决

暗绯莎

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。。。不会做。。。

暗绯莎

恩，恩，了解了
主要是没有算到最后，想想两个方程四个未知数肯定算不出来的。。。