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  3. Each employee of a certain company is in either Department X or Department 7, and there are more than twice as many employees in

Each employee of a certain company is in either Department X or Department 7, and there are more than twice as many employees in

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问题 Each employee of a certain company is in either Department X or Department 7, and there are more than twice as many employees in Department X as in Department Y. The average(arithmetic mean)salary is $25,000 for the employees in Department X and $35,000 for the employees in Department Y. Which of the following amounts could be the average salary for all of the employees of the company?
Indicate all such amounts.
A $26,000
B $28,000
C $29,000
D $30,000
E $31,000
F $32,000
G $34,000
选项
答案A，B
解析 One strategy for answering this kind of question is to find the least and/or greatest possible value. Clearly the average salary is between $25,000 and $35,000, and all of the answer choices are in this interval. Since you are told that there are more employees with the lower average salary, the average salary of all employees must be less than the average of $25,000 and $35,000, which is $30,000. If there were exactly twice as many employees in Department X as in Department Y, then the average salary for all employees would be, to the nearest dollar, the following weighted mean,
≈ 28,333 dollars
where the weight for $25,000 is 2 and the weight for $35,000 is 1. Since there are more than twice as many employees in Department X as in Department Y, the actual average salary must be even closer to $25,000 because the weight for $25,000 is greater than 2. This means that $28,333 is the greatest possible average. Among the choices given, the possible values of the average are therefore $26,000 and $28,000.
Thus the correct answer consists of Choices A($26,000)and B($28,000).
Intuitively, you might expect that any amount between $25,000 and $28,333 is a possible value of the average salary. To see that $26,000 is possible, in the weighted mean above, use the respective weights 9 and 1 instead of 2 and 1. To see that $28,000 is possible, use the respective weights 7 and 3.
This explanation uses the following strategies.
Strategy 1: Translate from Words to an Arithmetic or Algebraic Representation
Strategy 8: Search for a Mathematical Relationship
Strategy 12: Adapt Solutions to Related Problems
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