Ask a math problem for the first year of junior high school!! Speed!!! I m about to sleep!!!!!

Solution: This is a very classic question.

The key to the answer is that in 20 minutes, the correspondent first catches up with the first person in the same direction, that is, he travels the length of the entire line (this time is x (15-9)). Then they move in opposite directions, and walk the length of the line with the last person in the line (this time is x (15 9)).

So the length of the line is:

kilometers) of course it is best to solve it with a program:

Set the length of the team to x km.

According to the meaning of the equation:

x (15 9) x (15 9) 20 60 solve: x

A: The length of the team is kilometers.

Jiangsu Wu Yunchao wishes you progress in your studies.

Assuming the length of the team is x.

x/(15-9)+x/(15+9)=20/60x=

If the speed of returning to the end of the line after sending it is also 15km h.

x 6 + x 24 = 1 3 hours.

Find x and you're good to go.

The marching speed is 150 m min correspondent 250 m min.

Set the team length x x (250-150) + x (250 + 150) = 20

4x+x=20*400 5x=8000 x=1600 meters.

a= —,a2=2 3,a3=3,a4=-1 2,=> from the third number after the opening of the mold book to check the beginning of the cycle of the eggplant, 2003 divided by 3 the remainder is 2, Ziwei then a2003=2 3, 2004 and 3 are divisible, then a2004=3

Solution: If the width is x, the length is 2x

So c=2x

x²=c/2

x=√(c/2)

If the product of a rectangle is c and the length is twice the width, then the width of the rectangle is (c 2).

6x-6y-2x-2y-4x+4y+4x+4y

4x just remove the parentheses and simplify.

1.Set: Clothes are worth x credits. From the meaning of the title:

x+10）/12=（x+2）/7

Solution: x=2Set: The price of the product is X yuan. From the meaning of the title:

x - 250=250 *

Solution: x=320

3.Set: There are x products per box. From the meaning of the title:

8x+4) 5 =(11x+1) 7 + 1 solves x=12

4.Set: After x hours, the speed of the two cars is equal. From the meaning of the title:

30+20x = 90-10x

Solution: x=2

At this time, the speed is: 30 + 20 * 2 = 70

5.Set: The per capita quota for this month is x pieces. From the meaning of the title:

4x+20）/4=（6x-20）/5

Solution: x=45

Set: The per capita quota for this month is x pieces. From the meaning of the title:

4x+20) 4=(6x-20) 5 +2 solution: x=35

Set: The per capita quota for this month is x pieces. From the meaning of the title:

4x+20) 4=(6x-20) 5 -2 solution yields: x=55

6.Suppose: The lifespan of Diophantus is x years. From the meaning of the title:

1 6 + 1 12 +1 7 + 1 2)* x +5+4=x, the solution is: x=84

From the inscription, it can be obtained: 84 * 1 6 + 1 12 + 1 7) +5 = 39

From the inscription: 84 - 4 = 80

It is not difficult to see that from A to B is a headwind This is.

The speed is the aircraft speed + wind speed from b to a is downwind, which is the speed of the aircraft - the wind speed.

That is, aircraft speed + wind speed = 4000

Aircraft speed - wind speed = 4000

The sum of the two formulas yields 2 times the speed of the aircraft = 4000 + 4000 and the speed of the aircraft = 692km h.

Substituting the airplane speed = 692 km h into any of the above formulas, the wind speed = 77 km h.

That's it, huh

The airplane flies in this wind belt at a speed of x kilometers per hour, X-4000

x=9000/13

The airplane flew at a speed of 9000 13 kilometers in this wind belt.

Solution: Let the speed of the aircraft be xkm h and the wind speed be ykm h:

then 4000

, x=692km h, y=77km h

Let's assume that the speed of the aircraft is x kilometers per hour.

then X-4000

Solution: x = 692 km h.

The wind speed is 77 km/h.

Solution: Set the plane flat.

The average speed of Bai is duxkm h and the wind speed is ykm h.

From the meaning of the title, it can be seen that the dao arrives from place a.

There is a headwind in the inner B place, and a tailwind from the B place to the A place. Columnable capacity equations:

Got: x, y

1 Seats 45.

X cars, that is, 60 passenger cars have X-1 cars. The total number of people is y

Column: 45*x=y;

60*(x-1)-30=y

y=270, x=6

Rent a 45-seater coach and a 60-seater coach with A+1.

45a+60(a+1)>=270

a>=2, i.e. 2 cars for 45 seats and 3 cars for 60 seats.

The rent is 250 * 2 + 300 * 3 = 1400 yuan2, whether it is driving in the opposite direction or leading to the direction, the relative displacement of the two cars in the crossing time is the sum of the length of the two cars.

Assuming that the speed of the truck is 3a and the speed of the passenger car is 5a, there is:

5a-3a)*60=280+200, solution:

a=4 i.e. the speed of the truck is 12m s and the speed of the passenger car is 20m s When the two cars are driving in the opposite direction, there is:

12+20)*t=280+200, solution:

t = 15s3 assumes that x m long tops need to be made, (600-x) m long pants 2x 3 = (600-x) multiplied by 3 3

x=360 should be made of 360 meters of fabric for tops and 240 meters of fabric for pants to match 240 sets.

Set: each piece of clothing x m, each piece of pants y

2x=33y=3

The solution yields x=, y=1

600 sets.

240*m 240*1=240m.

4 solution: Set B to sell knife holder x blade 50x

The equation is: (1-5)x+(50x)*(

4x+25x=8400

21x=8400

x=400 Answer: Field B sold 400 knife holders.

Directly solve the second problem: the relative displacement (driving distance) of the farmer's and herdsmen's vehicles because the passenger car has to cross the truck from behind

Yes The sum of the length of the passenger car and the truck i.e. 280 + 200 480m for 1 minute and the relative speed is: 480 60 8m s

Then it is calculated that the passenger car is 8m s faster than the truck, and assuming that the speed of the passenger car is x, then there is x (x-8)= 5 3

If the solution is x 20ms, then the truck is 12ms

If you travel in the opposite direction, the distance is 480 m, and the known speed is 20+12 32 m s

The time taken is s v= 480 32 15 seconds.

Let the number of people be x

Then: x 45=(x+30) 60+1

x=270 people.

It is cheaper to take a 60-seater car.

If you want to be cheaper, the more 60-seater cars the better (provided that there are no vacant seats as much as possible) If you rent 5 60-seater cars, it will cost 300 * 5 = 1500 yuan, if you rent 4 60-seater cars and 1 45-seater car, it will cost 300 * 4 + 250 * 1 = 1450 yuan.

If you rent 3 60-seater cars and 2 45-seater cars, it will cost 300 * 3 + 250 * 2 = 1400 yuan (there are just no empty seats at this time).

The cheapest option is: rent 3 60-seater cars and 2 45-seater cars, which costs 1400 yuan and sets the speed of the truck to 3x meters in minutes.

The speed of the coach is 5x meters min.

The passenger car passed the truck and walked 280 + 200 = 580 meters.

Then: 580 (5x-3x)=1

x=290 The speed of the wagon is 870 meters min.

The speed of the bus is 1450 meters min.

If driving in opposite directions, the crossing time is: 580 (1450+870)=1 4 minutes = 15 seconds.

To make a blouse, you need fabric and rice pieces.

To make pants, you need 1 meter of fabric.

Let's make x sets of clothes.

x = 240 360 meters of fabric for making clothes, 240 meters of fabric for making pants, can be made into 240 sets of clothes Manufacturer B sold x knife holders and 50x blades.

The profit obtained by factory B is: (1-5)x+50x(

The profit obtained by Factory A is: 8400 (

According to the title: (1-5)x+50x(

x=400 Factory B sold 400 tool holders.

1. Solution: If you rent 45 passenger cars separately, you can rent 60 passenger cars (x-1) separately.

45x=60（x-1）-30，x=6；There are a total of 45 * 6 = 270 (people) of teachers and students.

In addition, there are 45-seat passenger cars Y in the scheme, and 60-seat passenger cars (Y+1).

45y+60（y+1）=270，y=2；250 * 2 + 300 * 3 = 1400 (yuan) < 250 * 6 = 1500 (yuan).

A: According to this scheme, the rent is 1,400 yuan.

1.If the number of 45 seats rented separately is x, then there is 45x=60(x-1)-30, and if x=6 is obtained, then the total number of people is 6 45=270, and 45 seats are rented separately.

The fee is 250 6 = 1500, and the cost of renting 60 seats alone is 300 5 = 1500, at this time, the number of 45 seats is y, then the number of 60 seats is y + 1, and the total rent is 250 y + 300 (y + 1) = 550 y + 300, according to the meaning of the topic: 550y + 300 < 1500, 45y + 60 (y + 1) 270, then you can get: 2 y 24 11, then select y = 2, the total rent is 550 2 + 300 = 1400 (yuan).

2.Suppose the truck speed is 3x meter seconds, and the passenger car speed is 5x meter seconds, then according to the subject there are (5x-3x) 60 = 280 + 200, find it x = 4, then the truck speed is 12 meters second, the passenger car speed is 20 meters second, then the opposite direction travel time is 480 (12 + 20) = 15 (seconds).

3.If x meters of fabric is used for the top, then the fabric for the pants is (600-x) meters, then according to the title:

x 3) 2=((600-x) 3) 3, find it: x=360 meters, then the fabric used to make the jacket is 360 meters, and the fabric used to make the pants is 240 meters.

4.(The cost of a new razor holder shouldn't be 5 yuan, right?) ）

Solution: The profit of factory A is 8400 (yuan), then the profit of factory B at the same time is 4200 2 = 8400 (yuan), and the number of tool holders sold by factory B is x, then the number of blades is 50x, then there is 50x the cost of tool holders) = 8400;

Bring in the data to solve and you'll get the answer.

Among them, 60 passenger cars are rented more than 45-seater buses??? What does this phrase mean.

The sum of odd fractions is even: 1 out of 3 + 2 out of 3 is 2 out of 15

The sum of 7 is 3

The sum of 9 is 4

Sum of even-numbered fractions: The sum of 2 fractions is 1 2

4 out of 1 is 1+1 2

6 out of 2 + 1 2

8 out of 8 is 3+1 2

10 out of 4 + 1 2

A total of 12+1 2

and for 22 and 1 2

(1) Xiaogang's family played in tourist attractions for 4 hours?

2) Find the speed on the return journey as = (180-120) (15-14) = 60 km/h.