求助 pp数学ds题，不明白~

michelle77

还有几天就考试了，不明白的prep错题麻烦大家帮忙看下

(1)Each employee on a certain task force is either a manager or a director. What percent of the employee on the task force are directore?

        1) The average (arithmetic mean)salary of the managers on the task force is $5,000less 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.

key C

(2)   If n is a positive interger less than 200 and 14n/60 is an integer, then n has how many different positive prime factors?

    2 ，    3。  5。  6。  8。    

key  3

[此贴子已经被作者于2009/8/13 22:17:22编辑过]

sophiaruan

(1)设经理有M个，平均工资为S1，总监有D个，平均工资为S2，所有人的平均工资为S

条件一：S1+5000=S 条件二：S2-15000=S

S=（S1M+S2D）/M+D第一个式子代进去得到一个等式：S1D+5000（M+D）=S2D，第二个式子代进去：S2M-15000（M+D）=S1M

两个式子得出：D：M=1：3 选C

（2）14N/60是个整数，说明7N/30是个整数，7不是30的因数，说以N是30的倍数，那么N可以是30，60，90，120，150，180

不管是那个数，起质因数都只有：2，3，5三个素数。key：3

michelle77

明白了！    谢谢sophiaruan