A 3.5-meter-long car is driving at a speed of 32 meters per second. In front of it is a 16.5-meter-long truck driving in the same direction at a speed of 27 meters per second. How many seconds does it take for the car to catch up with the truck?

A 3.5-meter-long car is driving at a speed of 32 meters per second. In front of it is a 16.5-meter-long truck driving in the same direction at a speed of 27 meters per second. How many seconds does it take for the car to catch up with the truck?

(16.5+3.5)/(32-27)=20/5=4
It takes four seconds for the car to catch up with the truck

A car with a length of 3.5 meters is driving at the speed of 45 meters per second, and a large truck with a length of 16.5 meters is driving in the same direction at the speed of 35 meters per second
Lie equation

Let x seconds exceed the truck
（45-35）x=3.5+16.5
10x=20
x=2

From the first place to the second place, the bus needed to run for 7 hours. Since the expressway was opened, the average speed increased by 20 kilometers per hour
Now it only takes 5 hours to get from place a to place B

Suppose the original speed of the bus is x km
（x+20）×5=7x
5x+100=7x
2x= 100
x=50
50 × 7 = 350 (km)
A: the distance between a and B is 350 kilometers

After the opening of the expressway, the bus speed has increased by 30 km per hour,
It only takes 4 o'clock to arrive, and the length of the expressway between a and B is calculated;

The distance between a and B is 320km. The original distance is 350km, and the speed is 50km / h, so it needs to drive 7h. After opening the expressway, the distance is 320km, and the speed is 80km / h. It needs to drive 4H