[問題]天山數學5-35

[mark-alan]

Station X and Y are xonnected by two separate, staright, parallel rail lines that are 250 miles long. Train P and Train Q simultaneously left station X nad and Station Y, respectively and each train traveled to the other's point of departure. The two trains passed each other after traveling 2 hours. When the two trains passed, which train was nearer to it's destination?

(1) At the time when the two trains passed, train P had and average a speed of 70 miles per hour.
(2) Train Q averaged a speed of 55 miles per hour for the entire trip.

我寫D 答案是A 還是C啊?

[汪汪北鼻]

1) At the time when the two trains passed, train P had and average a speed of 70 miles per hour.
(2) Train Q averaged a speed of 55 miles per hour for the entire trip.

1) sufficient p走了 70*2=140 剩 250-140=110，Q 則還有140 , thus p離車站近

2)insufficient 只說average speed ,也許前面speed >50 , 後面speed<50

thus, the answer is A

[chris8888]

(1) At the time when the two trains passed, train P had and average a speed of 70 miles per hour.
=> 此處表明average ... per hours, 所以火車走了140 miles, 才愈見另一台火車, 因此充分

(2) Train Q averaged a speed of 55 miles per hour for the entire trip.
=> 此句強調average ... for the entire trip, 表示速度不確定, 會變, 所以不能推算到底它走了多少, 只知道整個路呈平均時速而已