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标题: 求教：涛涛数学13-Q35 [打印本页]

作者: maggie88421 时间: 2009-7-31 18:08
标题: 求教：涛涛数学13-Q35

拜托各位G友帮我看一下这道题，感激不尽啊！

Q35:

Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination?

(1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour.

(2) Train Q averaged a speed of 55 miles per hour for the entire trip.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

为什么答案是A啊？请指教

作者: k_wang_2008 时间: 2009-7-31 18:26
(1) 相遇时P已经走了140 miles,离目的地还有110 miles;而此时Q离目的地还有140 miles.
(2) 由全程平均速度无法判断起初两个小时走了多少路程,题目没说全程匀速.

作者: ZH280113 时间: 2009-7-31 18:29

因为前两个小时的平均速度为70，证明相遇时Q车离P车的出发点（因为是相向而行，P的出发点也就是Q的终点）有140的距离。

因为两地相距250，所以可以判断出这时P车离终点近。

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