Solution: A is 3+3+3=9 minutes later than B.
Think of the whole distance as 1.
Then the speed of a = 1/30.
Speed B = 1/20
When Party A packed up and set out, Party B had already left 1/20×9=9/20.
Then the distance between Party A and Party B is1-9/20 =11/20.
The sum of the speeds of Party A and Party B =1/20+1/30 =112.
Then meet again in (11/20)/(112) = 6.6 minutes.
7. two cars, a and b, start from place a and drive in the same direction. A walks 36 kilometers per hour and B walks 48 kilometers per hour. If car A leaves two hours earlier than car B, how long will it take for car B to catch up with car A?
Solution: distance difference = 36× 2 = 72km.
Speed difference = 48-36 = 12km/h
It takes 72/ 12=6 hours for car b to catch up with car a.
8. Party A and Party B respectively set out from ab, which is 36 kilometers apart, and walked in opposite directions. When Party A departs from A to 1 km, it has been in A until it finds something and returns immediately. After the goods were gone, he immediately went from place A to place B, where Party A and Party B met. He knew that Party A walked 0.5 kilometers more than Party B every hour and asked both of them to walk.
Solution:
A actually walked 36× 1/2+ 1× 2 = 20km when they met.
B walked 36× 1/2 = 18km.
Then A walked 20- 18 = 2km more than B.
Then the meeting time =2/0.5=4 hours.
So A = 20/4 speed = 5 km/h.
Speed B = 5-0.5 = 4.5km/h/h.
1 1. Two cars A and B are driving in opposite directions at the same time from two places 600 kilometers apart. It is known that car A travels 42 kilometers per hour and car B travels 58 kilometers per hour. How many kilometers did B car travel when they met?
Solution:
Speed sum =42+58= 100 km/h
Meeting time =600/ 100=6 hours.
When they met, B traveled 58×6= 148 km.
or
The speed ratio of car A and car B is 42: 58 = 21:29.
So when we met, B traveled 600×29/(2 1+29)=348 kilometers.
12, the two cars are facing each other, and meet in six hours. Four hours later, the bus arrived, and the van was still 188 kilometers away. How far is the distance between the two places?
Solution: treat the two cars as a whole.
65438+ 0/6 of the whole journey of two cars per hour
4 hour line 1/6×4=2/3
Then the whole journey =188/(1-2/3) =188× 3 = 564 km.
13. The distance between Party A and Party B is 600 kilometers. The bus and truck traveled in opposite directions from two places and met for six hours. As we all know, the speed of a truck is two-thirds that of a bus. What is the speed of the two cars?
Solution: the sum of the speeds of two cars = 600/6 =100 km/h.
Bus speed =100/(1+2/3) =100× 3/5 = 60 km/h.
Freight car speed = 100-60 = 40km/h
14. The rabbit and the kitten walked in opposite directions from A and B, which are 40 kilometers apart, respectively. Four hours later, they met for four kilometers. How long did it take to meet again?
Solution: velocity sum = (40-4)/4 = 9 km/h.
Then it will take 4/9 hours to meet.
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