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
我选E错了,但是不知道怎么错的,请大家帮帮忙!
答案是B
根据题目,可以得出0<x<10,结合条件二,Z=5X,那么得出0〈X〈2,根据题目,可以得出X=1
根据求的问题,可以充分否定回答。
From (1), the arithmetic mean point of X and 10 sits at the middle of the segment from X to 10.
If Z sits between X and 10 and it is nearer to 10 than to X.
Then it can be concluded that Z>1/2(X+10).
If Z sits right to 10, definitely it is greater than 1/2(x+10).
So (1) alone is sufficient.
From (2), [Z-1/2(x+10)]=[5x-1/2(x+10)]=[(9x-10)/2], the result depends on value of X. So (2) alone is not sufficient.
I think A is correct.
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