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.
D=No. of directors, M=No. of managers, Ad=the average salaries of directors, Am=the average salaries of managers, ask for D/(D+M). Ad-Am=20000. Ad-15000=(Ad*D+Am*M)/(D+M)=Ad*D/(D+M)+Am*M/(D+M)=Ad*D/(D+M)+(Ad-20000)*(1-D/(D+M)=Ad*D/(D+M)+Ad-Ad*D/(D+M)-20000+20000*D/(D+M)=Ad-20000+20000*D/(D+M). D/(D+M)=5000/20000=1/4 考试时，碰见这种题，认倒霉吧
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发表于 2010-4-9 22:50:30
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