13. Two cars, A and B, start from AB at the same time and drive in opposite directions. The speed ratio of A and B is 4: 5. After the two cars met for the first time, the speed of A increased by a quarter, and the speed of B increased by a third. The two cars returned immediately after arriving in Pakistan respectively. In this way, the second meeting point is 48 kilometers away from the first meeting point, and how many kilometers away is AB?

Solution:

Think of the whole journey as a unit of 1

Because time is constant, the distance ratio is the speed ratio.

So when they met, A did the whole journey of 1x4/(5+4)=4/9.

Line B 1-4/9=5/9

At this time, Party A and Party B accelerate, and the speed ratio changes from 4: 5 to 4 (1+1/4): 5 (1+1/3) = 5:10/3 = 3: 4.

The sum of the distances that A and B meet again is twice the distance of AB, which is 2.

At this time, we met for the second time, and the whole journey of Party B was 2x4/(3+4)=8/7.

The distance of the second intersection is 8/7-4/9=44/63 of the total distance.

Distance to the first meeting point is 44/63-4/9= 16/63.

AB distance = 48/(16/63) =189 km.

14, A goes from place A to place B, and B and C go from place B to place A, all of which start at the same time. A meets B first, 15 minutes later meets C again. Take 70m for A, 60m for B and 50m for C.. Find the distance between AB and the solution: the speed difference between AB and C =60-50= 10 m/min, then when A and B meet, the distance from C = (70+50) ×15 =1800 m, then the time it takes for A and B to meet =/kloc.

15, Party A and Party B start to climb the mountain from the foot of the mountain at the same time, and go down the mountain immediately after reaching the top. Both of them went down the mountain twice as fast as themselves. When Party A reaches the top of the mountain, Party B is 500 meters away from the top. When Party A returned to the foot of the mountain, Party B just walked down the mountainside to find the distance from the foot of the mountain to the top of the mountain. Solution: Downhill speed is twice as fast as uphill speed. We assume that the downhill road is also regarded as the uphill road, and the speed of the uphill road 1/2 is the uphill speed. Then, the distance up the mountain accounts for 2/3 of the total distance, and the distance down the mountain accounts for 1/3 of the total distance. A returned to the foot of the mountain, and the whole journey of Otsuichi * * *: 2/3+65, 438+0/3 × 65, 438+0/2 = 5/6 B reached the top of the mountain at the speed of A, that is to say,