[讨论]prep-147（请教NN）

147.
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                      C答案
                这道题目我选择e,因为我实在推不出来，最后还有未知数存在。

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.

  想问一下 ；

 $5,000 less than the average salary of all employees on the task force. 是 mx/x=5000<(mx+dy)/(x+y)  还是

 mx/x+5000=(mx+dy)/(x+y) 

怎么求解

上来也是被蒙了一下，仔细读一下句子，应该是第二种说法吧，如果是第一种，是不是应该加个逗号。

解：设manager的工资为M，人数为X，director的工资为D，人数为Y

由题意得：M+5000=(MX+DY)/(X+Y)

          D-15000=(MX+DY)/(X+Y)

则先可求出 M=D-20000

将其带入第一个方程，则D-20000+5000=(DX+DY-20000X)/(X+Y)=D-20000X/(X+Y)

因此X/(X+Y)=15000/20000=75%，即题目所求