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Math trip in the sixth grade of primary school
1. Because the speed ratio is equal to the distance ratio in the same time, the speed ratio of Party A and Party B is 5: 4 at the time of departure, and the distance ratio of Party A and Party B is 5: 4 at the time of meeting. After the meeting, Party A's speed decreased by 20% and Party B's speed increased by 20%. Know the speed ratio after the meeting, and get the distance ratio after the meeting, so as to calculate.

Solution: When meeting, the whole journey of Party A is 5÷(4+5)=5/9, and the whole journey of Party B is 1-5/9=4/9.

After meeting, A arrived at B, and A walked 4/9 of the whole journey.

After meeting, the speed ratio of Party A and Party B is 5× (1-20%): 4× (1+20%) = 4: 4.8 = 5:6, that is, the distance ratio is 5: 6.

So after meeting, A arrived at B, and the corresponding B traveled 4/9*6/5=8/5 of the whole journey.

So general manager b went all the way.

4/9+8/ 15=44/45

There is still 1-44/45= 1/45 in the whole journey.

So the distance between AB is 10÷ 1/45=450 (km).

A: The distance between a:AB and Shanghai is 450 kilometers.

2. This problem is mainly about drawing figures and listing equations.

Let the speed of b be v and the distance between a and b be s.

According to the condition that A catches up with B for the first time, it shows that A runs faster than B, and the gap between them is S from the beginning.

In this way, the first equation 240*V+S=3*240 (the first encounter, the right side represents the distance that A runs in four minutes, and the left side represents the distance that B runs in four minutes, plus the difference between them. So that the two sides can be equal). After the meeting, Party A and Party B are now in the same place. At the second meeting, Party A was 400 meters faster than Otsuichi Circle, and the second equation was 600V+400=600*3.

V=7/3 S= 160 is obtained from the above two equations.

Answer: The speed of B is 7/3 sec/m, and the distance between A and B is 160 km.

3. The speed ratio of Party A and Party B is 3: 5.

"It is known that the speed of C is faster than that of A 1/9", which means that the speed ratio of A is 9: 10, that is, the speed of A is 9/ 10 of C. 。

It can be seen from the above that the speed ratio of ethylene to propylene is 3: 2.

600×2÷(3+2)×2

= 1200÷5×2

=240×2

=480KM When A, B and C meet, A and C's journey.

480×( 1-9/ 10)÷2

=480× 1/ 10÷2

=48÷2

= 24 km/h