1. A truck drives from place A to place B at a speed of 30 kilometers per hour. 1 hour later, car A also drove from place A to place B at a speed of 50 kilometers per hour, and arrived at place B half an hour earlier than the truck. Find the distance between a and b.

Answer: The truck is longer than the car 1+0.5 = 1.5 hours, the truck is ahead 1.5× 30 = 45 kilometers, and the car takes 45 ÷ (50-30) = 9/4 hours to complete the journey, so the distance between the two places is 50× 9.

2. On Children's Day, the students went for a spring outing, marching at a speed of 1 meter per second. The team is 300 meters long. Teacher Wang chased from the end of the team to the end of the team at a speed of 1.5 meters per second because of something, and immediately returned from the end of the team to the end of the team. How many minutes will it take * *?

It takes 300 ÷ (1.5- 1) = 600 seconds to answer from the end, and 300 ÷ (1.5+1) =120 seconds to answer from the end, * * needs.

There are three cars, A, B and C, and each car runs from A to B at a certain speed. B starts later than C 10 minutes, and catches up with C after 40 minutes; A leaves 20 minutes later than B and catches up with B in 50 minutes. So, how long will it take for A to catch up with C after it starts?

The speed ratio of solutions A and B is (50+20): 50 = 7: 5, that of solutions B and C is (40+ 10): 40 = 5: 4, and that of solutions A and C is 7: 4. When A catches up with C, C takes longer than A 10+20 = 30 minutes.

My sister walks at a speed of 75 meters per minute, and my sister walks at a speed of 65 meters per minute. After the elder sister left for 20 minutes, the elder sister followed her. How many minutes will it take for my sister to catch up with her? How many meters are there from the starting point at this time?

Answer: My sister is 20× 65 = 1300m ahead, and when I catch up with her, she is in front 1300m, and my sister is 75-65 = 10m per minute, so my sister is from1300 ÷10.