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
--------------------------------------------------------------------------------------------
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
欢迎光临 ChaseDream (https://forum.chasedream.com/) | Powered by Discuz! X3.3 |