求~数学题一道~

BlackTTea

If x is apositive number less than 10, is z greater than the average (arithmetic mean)of x and 10 ?
(1) Onthe number line, z is closer to 10 than it is to x.
(2) z = 5x
答案是A，但我算的是E。答案的解释是： (1)得知 10-Z < Z-X， 得出 2Z > 10 +X ← 選項(1)成立。  我觉得A只能得出|z-10|<|z-x|的结论啊。~题目没有说明z在10和x之间啊。。困惑~请各位指教。。

zafteria

(1) if z>=10 clearly right
     if z<10  10-z<z-x , so z>1/2(10+x)
so (1) alone can answer the question

BlackTTea

(1) if z>=10 clearly right
     if z<10  10-z<z-x , so z>1/2(10+x)
so (1) alone can answer the question

-- by 会员 zafteria (2010/10/18 12:16:44)

原来是这样~我没考虑周全。。谢谢啦~