求助？

wujie_rens

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！

meimei5656

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.

freesimens

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。