GWD 13-35 请教

echoetmoi

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.


我选了　Ｄ　，　理由如下，ａ　说了　在相遇前ｐ的速度，所以相遇点为　ｐ的速度乘２　．求出具体点．可得具体位置

ｂ　说Ｑ的全程速度，平均速度．那么相遇点位　Ｑ*２ 距离它的出发点的具体位置，　也可以求出具体位置，ｓｏ，　应该为Ｄ答案阿



前面ｎ多牛　说　为　Ａ　，为什么Ｂ不行啊？



请教数学高手．　（我觉得低手也能做这道题阿)

Knightll

A你如果同意，就不解释了。

B为什么不行呢，因为，只提供整个旅程的平均速度，那么可能相遇前Q走得很慢，相遇后以10倍的速度跑。反之，亦然。所以不能判断他们相遇的距离到底距离终点多远。错。

atlantiswind

呵呵，总算明白了

lanshi

题中说的parallel rail lines that are 250 miles long,是不是指两条线路每条250米长。还是说一共250米长。

如果是第一种说法的话，我觉得A应该是求不出来的。因为不知道另一个的速度。我是不太明白为什么选A。

cher6068

条件2, 是不是匀速行驶的意思呢, 如果是的话, 答案就应该选D呀. 请NN指教, 谢谢!

nokidding

条件2的意思是Q的全程平均速度是55，不是匀速行驶的意思，所以光凭条件2不能选出答案

sayyessi

I choose A because if train P had averaged a speed of 70 miles per hour, then since two hours had passed,  2*70 is 140 miles.  So P had already traveled 140 miles, the whole track is only 250 miles.  So P traveled way passed the midpoint and thus nearer to its destination?  

Choice B provides no information about the average speed for the 1st two hours.

sabineceng

没看到是全程速度！！晕死

songxueb

A也不一定阿，只是说相遇时Ａ是７０，相遇前的不知道啊，可能很低，到了相遇时达到７０，那就不能按照７０＊２＝１４０来算了吧

sisleycheerup

1说的是相遇时A的平均速度是70，不是相遇的那一刻的速度。