If X is a positive number less than 10, is Z greater than the average (arithmetic mean) of X and 10 ?
(1) On the number line, Z is closer to 10 than it is to X.
(2) Z = 5X
答案是A.
能不能解释下思路.
举报
画数轴,两种情况,一种z在10右边,一种在左边,都能推出的
0<x<10 => Z> (x+10)/2?
1) 数轴上,“Z is closer to 10 than it is to X” =〉 Z〉x+(10-x)/2= (10+x)/2 (画图后更清晰)
2)Z= 5X => Z- (x+10)/2= 5x-(x+10)/2 = (9x-10)/2
0<x<10 => -5 <(9x-10)/2 <40 => Z不一定比(10+x)/2 大
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