Math JJ, 急??? 在线等

117. A certain list consists of 3 different numbers.  Does the median of the 3 numbers equal the average (arithmetic mean) of the 3 numbers?

(1)   The range of the 3 numbers is equal to twice the difference between the greatest number and the median.

(2)   The sum of the 3 numbers is equal to 3 times one of the numbers.

选B

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B中"one of the numbers"不一定是y 吧?

谢谢

(1)设A<B<C

C-A=2(C-B)  --> A+C=2B 所以B是ABC的平均数  

(2)设X+Y+Z=3X

Y+Z=2X X=(Y+Z)/2 所以X是XYZ的平均数且X<Y<Z

总之，平均数＝中数时，数列各元素围绕中数中心对称；LZ可以画条数轴体会下