1, solution: Let the train speed be x m/s and the train length be y m. 。

From the topic: 45x=800+y

35x=800-y

Solution: x=20

y= 100

A: The train speed is 20 meters per second and the length is 100 meters.

2, speed and x2 = 20km; Speed difference ×2=2 km.

Solution: let the speed of a be xkm/h and the speed of b be ykm/h,

Judging from the title: 2(x+y)=20

2(x-y)=2

Solution: x=5.5

y=4.5

A: A's speed is 5.5 km/h and B's speed is 4.5 km/h. 。