PREP-DS-1-182 求解...

182.
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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.

答案: B

我选的C,不能理解B这个单独怎么能算出来的,

请高人指点迷津....

设三个人的annual salary分别为 M, J K

则有 M>J; M>K; M-J=2(M-K), 则(M+J+K)/3=(2K-J+J+K)/3=K/3