4. Party A and Party B walk from place A to place B at the same time. When Party A completes the whole journey of 1\4, Party B is still 640 meters away from B. When Party A completes the remaining 5\6, Party B completes the whole journey of 7\ 10. What's the distance between AB and place?

Solution: After A left 1/4, the remaining 1- 1/4=3/4.

Then the remaining 5/6 is 3/4×5/6=5/8.

At this time, a * * * left 1/4+5/8=7/8.

Then the distance ratio between Party A and Party B is 7/8: 7/ 10 = 5: 4.

So when A goes 1/4, B goes 1/4×4/5= 1/5.

Then AB distance =640/( 1- 1/5)=800 meters.

5. Two cars, A and B, start from A and B at the same time and drive in opposite directions. Car A travels 75 kilometers per hour, and it takes 7 hours for car B to complete the journey. Three hours after the departure of the two cars, the distance is15km. What is the distance between a and b?

Solution: Case A: Party A and Party B have not met yet.

3/7 of the 3-hour journey of the B train.

The three-hour journey is 75×3 = 225 kilometers.

AB distance = (225+15)/(1-3/7) = 240/(4/7) = 420km.

In one case, Party A and Party B have met.

(225- 15)/( 1-3/7)= 2 10/(4/7)= 367.5km。

6. One, two people should go this way. A It takes 30 minutes to walk and 20 minutes to walk. After walking for 3 minutes, A found that she didn't take anything, which delayed for 3 minutes. How many minutes does it take to walk from A to B?

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.

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