1. When the plane flies between two cities, it takes 55 minutes with the downwind and 1h with the headwind. Given that the wind speed is 20km/h, what is the flight speed of the plane?

Solution: let the actual speed of the aircraft be xkm/h.

(x+20)*55/60=(x-20)* 1

1 1/ 12x+55/3 = x-20

x- 1 1/ 12x = 55/3+20

1/ 12x = 1 15/3

x=460

2. The two trains A and B are 144m and 180m respectively. The train A runs 4m more per second than the train B ... The two trains are running in opposite directions. It takes 9 seconds from meeting to staggering. What's the speed of these two trains?

Let the speed of car B be x m/s, then the speed of car A is x+4m/s..

( 144+ 180)/(x+x+4)=9

324/(2x+4)=9

2x+4=36

2x=32

x= 16

One car: 16+4=20

Xiaoming and Xiao Li are classmates. The two of them set out from school to watch sports games in the playground. Xiaoming walks 80 meters every minute. He walked to the playground and waited for five minutes before the game started. Xiao Li walks 60 meters every minute. When she entered the playground, the game had already started for 3 minutes. How far is it from school to playground?

It's x meters from school to the playground.

x/60-x/80=5+3，

1/240x=8

x= 1920

It takes four hours for a ship to sail between two docks, and it takes eight kilometers to reach the other dock after sailing against the current for 4.5 hours. Assuming that the current speed is 2 kilometers per hour, find the distance between the two docks.

The speed of the ship in still water is x km/h.

4(X+2)=4.5(X-2)+8

4x+8=4.5x-9+8

4x+8=4.5x- 1

4.5x-4x=8+ 1

0.5x=9

X= 18

Distance 4× (18+2) = 80km.