8. Party A and Party B set out from A and B at the same time, and the place where they first met was 50 kilometers away from the midpoint. After arriving at B and A, Party A and Party B immediately turned around and walked back. So, Party A and Party B met for the second time at a distance of A 100 meters to find the distance between A and B..

Two people, A and B, set out from A to B, A can't, and B can ride a bike. If A walks 6 kilometers, they will arrive at B at the same time 45 minutes after B leaves. If A takes 1 poem first and B catches up with A half an hour after departure, find the distance between A and B. 。

Let the speed of a be a km/h and the speed of b be b km/h.

45 minutes =3/4 hours

6+3/4a=3/4b

a=(b-a)x 1/2

simplify

b-a=8( 1)

3a=b(2)

( 1)+(2)

2a=8

A=4 km/h

B = 3x4 =12km/h

AB distance = 12x 3/4 = 9 km.

9. The factory is connected with A and B by road and railway. This factory buys a batch of raw materials with a price of 1, 000 yuan a ton from A and sends them back to the factory, and makes products with a price of 8000 yuan a ton from B. It is known that the road freight 1.5 yuan/(tons, kilometers), the railway freight 1.2 yuan/(tons, kilometers), and these two.

10, Dong Zhang went to the department store to buy two types of envelopes, ***30, of which 1 50 yuan was used to buy type A envelopes and 1 50 yuan was used to buy type B envelopes. Each B-shaped envelope is 2 cents cheaper than the A-shaped envelope. What is the unit price of these two kinds of envelopes?

Let the unit price of type A envelope be one point, and that of type B envelope be -2 points.

If you buy a B-type A envelope, you will buy a 30-b-type B envelope.

1 yuan.50 = 150.

ab= 150( 1)

(a-2)(30-b)= 150(2)

By (2)

30a-60-ab+2b= 150

Substitution (1)

30a- 150+2b=2 10

30a+2b=360

15a+b= 180

b= 180- 15a

Replace (1)

a( 180- 15a)= 150

Answer? - 12a+ 10=0

(a-6)？ =36- 10

a-6= √26

a=6 √26

A 1≈ 1 1 min, then the b-type envelope 1 1-2=9 points.

A2≈0.9, then 0.9-2=- 1. 1 of the type B envelope is irrelevant, so it is discarded.

The unit price of type A is 1 1, and that of type B is 9.

1 1. It is known that a railway bridge is 1000 meters long and a train passes by. It takes 1 minute for the train to get on the bridge from the start point to the end point, and the whole train will get on the bridge completely for 40 seconds. What about the speed and length of the train?

Let the train speed be one meter per second and the car body length be b meters.

1 min =60 seconds

60a= 1000+b

40a= 1000-b

100a=2000

A = 20m m/s

b=60x20- 1000

B=200 meters

The car body is 200 meters long and the speed is 20 meters per second.