Junior high school math problems, now to ask, the first 150 reward

1.In the 400-meter circular runway, A and B will take a total of 400 (2+3)=80 seconds to meet at a speed of 2 m per second and 3 m per second respectively.

The puppy started running after 6 seconds, and ran for a total of 80-6=74 seconds.

The puppy (landlord) ran 6 meters per second, a total of 74 * 6 = 444 meters.

2.Length x m (640+x) m 108 km hr = sec.

Solvable equations. 108 kmh = 108 * 1000 m 3600 seconds = 30 m sec.

3.Set B speed x km h

The puppy's starting speed does not change after 6 seconds, and the distance it runs: 6x(80-6)=444 meters.

2. The length of the train is n meters, from the front of the train to the rear of the car: 640+n meters.

108 kmh = 30 m/s.

So the equation is: 640+n=

n = 215 meters.

The answer is that the puppy is 6 seconds later, that is, after the two have walked a total of 30 meters, that is, when the two are still 370 meters apart, the dog has been running, the key is to be, so the dog ran 370 (2+3) 74 seconds 6 74 444 meters.

2.Note that 108 km/h = 30 m sec 30 This is the distance the train travels, and the length of the train is 215 meters after removing the tunnel.

Let the length of the car be x, and the equation is 640+x 30

3.Is there something wrong with it, should it be immediately from place B, and the two meet? Or is it a total of time? The time is 4h

Question 2: 108 km h = 108 m s = 30 m s

Let the length of the car x, (640+x) 30=

In fact, from the head of the train to the head of the train out)

Test Point: Application of Unary Equations Topic: Application Problem Analysis: First assuming that the car that needs 30 seats is x, and the equation can be listed according to the number of people Solution: Solution: Suppose the car that needs 30 seats is x, according to the question: 30x=40(x-1)-20, and the solution: x=6

Number of visitors = 30 6 = 180 (people).

Therefore, the number of people who visited the construction of the Three Gorges in the school was 180 Comments: The key is to find out the equiquantity relationship and solve the one-dimensional equation

Set up to rent x Liang 40-seater bus, if you rent a 30-seater bus, you have to rent x+1 car.

Column equation: 40x-20=30 (x+1).

x = 5 with 180 people.

Set up car rental x cars.

30x=40(x-1)-20

x=630x=180

The number of visitors to the Three Gorges construction project at the school was 180.

The second is the time it takes for the two to meet for the first time.

2. After the first encounter, the two went against each other, and when they reached both sides, they swam a swimming pool long, that is, 90 meters, and then turned around and swam back, met again, and swam a swimming pool long, 90 meters, that is, the two people swam the length of two swimming pools from the first encounter and the second encounter, that is, 180 in the question, and each time they meet in the future, they must go against each other to reach both sides and then swim back to meet, that is, they meet after 36 seconds.

min is 180 seconds, minus the time of the first encounter, which is the time that two people can swim except after the first encounter.

4. The remaining 162 seconds divided by the time of each encounter is the number of subsequent encounters, because this time indicates that there were four encounters, but the fifth time did not meet, that is, there were four subsequent encounters.

5. The remaining time can meet four times plus the first encounter is five.

This kind of problem is mostly seen in Olympiad math problems, mainly to analyze each step in the problem clearly, generally speaking, the first day cup and the last day cup are different, and the middle steps are the same; The second is the processing of decimals, pay attention to whether to move forward one, or to round, such as the number of encounters in the question to appear decimal to be rounded, because there is no encounter, if you are looking for the number of square bricks, you have to go into one, because there is a gap in the number of bricks due to the lack of rounding.

Hope that helps.

a is the smallest positive integer.

The opposite of a=1b is still itself.

b = 0c is 3 greater than the largest negative integer

c=-1+3=2

2a+3c)*b

01 floor from the load.

-a 3-5 is the opposite of 2.

a/3=5-2=3

a=-9 b=-1/9

Original = -18 + 3 4 = -69/4

-a 3-5 is the opposite of 2, then a = -4

A and b are reciprocal to each other, then b = -1 4

So 2a+3 4ab=

The meaning of the topic is unclear, and there are many solutions.

a=-3 of the solution

So b=3

3*ab/2a+4=27/2

2.According to the title, a=1

b=0c=-1+3=2

2a+3c)*b

2a+3c)*0

Solution: The starting position of :( point c should be on the negative half axis of the x-axis. (1) Connect the OM.

Known as: a b ab

then omb = moa b = aoc

om = ob b = omb by moa = aoc

again om = oc oa = oa moa coa (sas).

oma = oca (= 90°), then om am in m am cut o in m

2) (It should be an analytic formula for am.) ）

In RT ACO, AOC = 60°, ACO = 90°, OC = 1

ac = √3

then a(-1, 3).

b = aoc = 60° ob = om mob is a regular triangle.

And ob = oc =1 , it is easy to get m(1 2, 3 2) and let the analytic formula of the straight line am be y = k x + b , then there is:

k + b = √3

1/2k + b = √3 /2

The solution is: k = - 3 3 b = 2 3 3, so the analytical formula is: y = - 3 3 x + 2 3 3

It is recommended that you go to our teacher Meng, who specializes in solving problems.

6 km per hour = 100 m in 1 minute

A line of A-meter-long team yards Pei Wu traveled at a speed of 6 kilometers per hour, and a student at the end of the team ran to the head of the team in 1 minute, and this Chi Maowei ran A+100 meters in one minute.