In a certain year, the difference between Mary's and Jim's annual salaries was twice the difference between Mary's and Kate's annual salaries. If Mary's annual salary was the highest of the 3 people, what was the average (arithmetic mean) annual salary of the 3 people that year?

(1) Jim's annual salary was $30,000 that year.
(2) Kate's annual salary was $40,000 that year.


Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

EACH statement ALONE is sufficient.

Statements (1) and (2) TOGETHER are NOT sufficient.

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题目解析：某年Mary和Jim的年薪之差是Mary和Kate的年薪之差的2倍。假如Mary的年薪是三人中最高的，问三人年薪的算术平均数是多少？
条件1：Jim的年薪是$30,000；
条件2：Kate的年薪是$40,000。
题目分析：我们设Mary的年薪是M，Jim的年薪是J，Kate的年薪是K，由题干可知：M-J=2（M-K）可以得到M+J=2K，其实M，K，J是由三个元素组成的等差数列，我们要求三者的算术平均数，只要知道M+K+J即可
分析条件1：我们只知道最小的J，而无法知道公差，所以无法确定M和K的大小，不充分
分析条件2：由于M+J=2K，那么M+K+J=3K=$120,000，充分。

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Prep2007E1-DS