[求助]一道GMATPP的DS

billchen_hikaru

   r         s      t

on the number line shown, is zero halfway between r and s?

1)s is to the right of zero

2)the distance between t and r is the same as the distance between t and -s

答案是B，请讲讲过程好吗？谢谢！

billchen_hikaru

谢谢你的分析！终于弄清了。 

billchen_hikaru

对不起，答案是C，不知道怎么求证的