GWD数学

feiming

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.
为什么这道题选第一个啊，我认为应该选第二个。。。

lzhch89

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.
为什么这道题选第一个啊，我认为应该选第二个。。。

-- by 会员 feiming (2011/5/7 22:45:09)

条件一是充分的，train P had, 意思是P、Q想与之前P的平均速度是70。因此可以推出P train 2小时走了140miles。也就是说P还有110miles到终点，Q还有140到终点。


条件二不充分,Q的entire trip的平均速度无法得知两车相遇之前两车的速度是如何，也就不能知道两车在哪一点相遇的。

feiming

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.
为什么这道题选第一个啊，我认为应该选第二个。。。

-- by 会员 feiming (2011/5/7 22:45:09)

条件一是充分的，train P had, 意思是P、Q想与之前P的平均速度是70。因此可以推出P train 2小时走了140miles。也就是说P还有110miles到终点，Q还有140到终点。


条件二不充分,Q的entire trip的平均速度无法得知两车相遇之前两车的速度是如何，也就不能知道两车在哪一点相遇的。

-- by 会员 lzhch89 (2011/5/8 0:40:23)

可是题目不是问的是相遇时，哪个离目的地更近么，通过第二个能求出当时从Q出发的火车已经行驶了110miles了，可见应该从P出发的火车离目的地更近啊