GMAT Prep

[weirdude]

please help.

[vantreal]

to know whether 0 is halfway between r and s
--> need to know whether l 0-r l = l s-0 l and r <0, s >0, which means r = -s, or s = -r

(1) s > 0
--> insufficient, s can be any number, it does not give me any relationship between r and s.

(2) l t - r l = l t - (-s) l
--> insufficient, we are not sure where 0 is, so we can not determine whether s is positive.

(1) + (2)
when s > 0, 0 is on the left hand side of s.
so l t - r l = t - r and l t - (-s) l = t +s,
t - r = t + s,
get rid of t,
now you can determine whether -r = s

Answer: (C)

[weirdude]

got it!
thank you very much!

[Philosophia]

還是想不透 (2)

因為 on the number line shown, t>s>r
所以若l t - r l = l t - (-s) l
when t<0 --> s<0, r<0, and s=r ==>impossible: t>s>r
when t=0 --> s<0, r<0, and s=r ==>impossible: t>s>r
when t>0 --> if s>0 and r>0 --> s=r ==>impossible: t>s>r
　　　　　　 　 if s<0 and r<0 --> s=r ==> impossible: t>s>r
　　　 　　　　 if s>0 and r<0 --> s=-r ==>zero is halfway between r and s

還是想不透為什麼答案是 C
因為在t>s>r的條件下，要滿足(2)，0 就會分別在 r 與 s 之間了，不是嗎？

[Philosophia]

還是想不透 (2)

因為 on the number line shown, t>s>r
所以若l t - r l = l t - (-s) l
when t<0 --> s<0, r<0, and s=r ==>impossible: t>s>r
when t=0 --> s<0, r<0, and s=r ==>impossible: t>s>r
when t>0 --> if s>0 and r>0 --> s=r ==>impossible: t>s>r
　　　　　　 　 if s<0 and r<0 --> s=r ==> impossible: t>s>r
　　　 　　　　 if s>0 and r<0 --> s=-r ==>zero is halfway between r and s

還是想不透為什麼答案是 C
因為在t>s>r的條件下，要滿足(2)，0 就會分別在 r 與 s 之間了，不是嗎？

請問有人可以幫我嗎？或是因為這篇舊文的標題下得不精確，大家都沒看到呢？...

[Philosophia]

可能是因為大家無法下載圖形，無法看到題目，所以我重新開版發問

附上連結http://www.chemy.idv.tw/phpbb2/viewtopic.php?t=29998