189.Each employee on a certain task force is either a manger or

a director. What percent of the employees on the task force are

directors?

1) The average salary of the mangers on the task force is $5000

less than the average of all employees on the task force.

2) The average salary of the directors on the task force is

$15000 greater than the average salary of all employees on the

task force.

Ans. C

谢谢！

根据条件，设本组average salary 为x，则根据条件1，2，

average salary of manager=x-5,000，average salary of

director=x+15,000;

设这一组manager人数为a， director人数为b，提干要求b/(a+b)

列方程：

(x-5,000)*a+(x+15,000)*b=x*(a+b)

打开，两边消掉x*(a+b)，就能求出a/b, 然后求出b/(a+b)

所以选C

谢谢 , 没想到式子一打开，就可以消掉那些复杂的东东，以为式子很复杂，就敢没去列式子了。看来以后要大胆的列出式子，可能没有想象的那么复杂。

谢谢！！