0.7: x = 15: & # 188; solution ratio

0.7: x = 15: & # 188; solution ratio

7 * (1 / 4) = 15x
So x = 0.7 * (1 / 4) / 15
=7/600

(6 / X-2) = (x / x + 3) - 1 to solve the equation

Multiply by (x + 3) (X-2)
6x+18=x²-2x-x²-x+6
6x+18=-3x+6
9x=-12
x=-4/3
The test shows that x = - 4 / 3 is the solution of the equation

2 (x + 1) ^ 2 / (x ^ 2) + (x + 1) / (x) - 6 = 0 to solve the equation

2 (x + 1) ^ 2 / (x ^ 2) + (x + 1) / (x) - 6 = 0 multiplied by x ^ 2
2(x+1)^2+x(x+1)-6x^2=0
2x^2+4x+2+x^2+x-6x^2=0
-3x^2+5x+2=0
3x^2-5x-2=0
(3x+1)(x-2)=0
x1=-1/3 x2=2

Mathematics problems in the second semester of the seventh grade
Deform the polynomial as follows: m ^ 4-m ^ 2 + 2n ^ 4-3m ^ 2n ^ 2 + 2mn-n-7
1. The fourth order items are put in the brackets with a + sign in front, and the second order items are put in the brackets with a "-" sign in front;
2. Put the first three items in the brackets with a "-" sign in front, and the rest items in the brackets with a + sign in front;
3. Put the items that only contain the letter M in the brackets with + in front, the items that only contain N in the brackets with - in front, and the rest in the brackets with - in front
To be quick, do not have no steps, to list the formula, do not just have results, good plus 50 points!!

1、+(m^4+2n^4-3m^2n^2)-(m^2-2mn)-n-7
2、-(-m^4+m^2-2n^4)+(-3m^2n^2+2mn-n-7)
3、+(0)-(n)-(-m^4+m^2-2n^4+3m^2n^2-2mn+7)

Xiao Li has 4 red beads and 15 yellow beads. She wants to make a necklace so that the number of yellow beads is three times that of red beads
(1) If the number of red beads remains unchanged, how many yellow beads need to be increased or decreased?
(2) If the number of yellow beads remains unchanged, how many red beads need to be increased or decreased?
I really don't understand this problem

(1) 15 △ 3 = 5 (pieces)
A: five more yellow beads are needed
(2) 5-4 = 1 (piece)
Answer: need to reduce 1 red bead
I have done this problem, but I don't remember it very well

60 cm is many meters

0.6

The school plans to paint the walls of four classrooms in grade five. Each classroom is 9 meters long, 6 meters wide and 4 meters high. The area of doors and windows is 4.4 square meters. How many square meters are there in total

We need to paint five surfaces
（9x6+6x4x2+9x4x2）x4
=（54+48+72)x4
=680
680-4.4x4
=680-17.6
=662.4

Mathematical problems, to write the formula, online, etc
1. 1 / 20 of a barrel of oil is poured out, which is exactly 10 kg. How many kg is the barrel of oil?
2. There are 150 lychee trees and 2 / 3 longan trees in the orchard. How many longan trees are there?
3. The perimeter of a square is 8 / 9 meters. How many square meters is its area?
4. There are 20 girls in class 53, accounting for 5 / 12 of the class. How many are there in class 53?

1.1
10 ÷ - = 200 (kg)
twenty
A: this barrel of oil is 200 kg
two point two
150 × - = 100 (trees)
three
A: there are 100 longan trees
3.8 2
- △ 4 = - (m)
9 9
2 2 4
- × - = - (M2)
9 9 81
four
A: the area is - square meters
eighty-one
four point five
20 - = 48 (person)
twelve
A: there are 48 people in class 53

2.5 * 10 ^ 3kg / m3 equals several grams / cubic centimeter

2.5 * 10 ^ 3 kg / m3 = 2.5 * 10 ^ 6 g / 10 ^ 6 cc = 2.5 g / cc

Solving application problems with 20 elementary equations

The practice of one variable equation of one degree
Key points: 1. Find out the equality relation; 2. Use the required unknown quantity (or indirect quantity) as the known quantity; 3. Express the equality relation with the algebraic formula containing the unknown number and the number. Then the equation is listed and the answer can be obtained after solving the equation
To remember: learn the truth, as long as the first time to learn the truth, later will be handy
1. A class of students went boating in an amusement park. They calculated that if one boat was added, there would be 6 people in each boat; if one boat was reduced, there would be 9 people in each boat. How many students are there in this class?
Equivalency: the number of students remains the same whether the number of ships is increased or decreased
Increase the capacity behind the ship = decrease the capacity behind the ship
Design x rowing vessels, the added vessels are (x + 1) and the students are 6 (x + 1)
The number of ships reduced to (x-1) and the number of students carried to 9 (x-1)
Countable equation: complete by yourself
Requirements: the answer process should be complete
2. 22 workers in a workshop produce bolts and nuts. Each worker produces an average of 1200 bolts or 2000 nuts per day. A bolt should be equipped with two nuts. In order to make the products just match each day, how many workers should be assigned to produce screws and how many workers should produce nuts?
Equal relation: a bolt should be equipped with two nuts, if the number of bolts × 2 = the number of nuts
If x persons are assigned to produce bolts, then (22-x) persons are assigned to produce nuts
X people produce 1200X bolts per day, (22-x) people produce 2000 nuts per day (22-x)
Countable equation: complete by yourself
Requirements: the answer process should be complete
3. How many hours does it take for a job to be completed by Party A alone for 20 hours and Party B alone for 12 hours?
The work problem is equal to the number of work done by Party A + the number of work done by Party B = 1
If a and B cooperate in the remaining part, it will be completed in X
A is dry () B is dry
Countable equation: complete by yourself
Requirements: the answer process should be complete
4. It takes 80 hours for a unit to plant trees by one person. Now some people plant trees for 5 hours first. Because the unit has an emergency, another 2 people have to complete the task within 4 hours. The work efficiency of these people is the same. How many people should be arranged to plant trees first?
Equal relation: the total working hours of planting trees are the same, that is, one person working hours = more than one person working hours
If x people should be arranged to plant trees first, then 2 people should be added, and then (x + 2) people should be planted
X man 5 hours + (x + 2) man 4 hours = one man 80 hours
Countable equation: complete by yourself
Requirements: the answer process should be complete
5. A, B and C donated books to children in poverty-stricken areas. It is known that the ratio of books donated by the three students is 5:6:9. They donated 320 books in total. How many books did the three students donate?
Equality: books donated by Party A + books donated by Party B + books donated by Party C = total number of books donated
Suppose one is x, then a donates 5x books, B C
Countable equation: complete by yourself
Requirements: the answer process should be complete
6. The sum of a two digit number and a ten digit number is 10. If the new two digit number is 18 larger than the original two digit number by exchanging the positions of the two digit number and the ten digit number, how about the original two digit number?
Equality relation: new number - original number = 18
Let X be the number in the original two digit number, then the number in the ten digit number is (10-x)
The new number is 10x + (10-x) and the original number is 10 (10-x) + X
Countable equation: complete by yourself
Requirements: the answer process should be complete
7. A company plans to organize employees to travel to a certain place on May Day. The service quality of a and B travel agencies is the same, and the price of organizing travel to the place is 300 yuan per person. When contacting the company, a travel agency says it can give 75% discount to each passenger, B travel agency says it can free one passenger's fee, and the rest 20% discount
(1) When the number of tourists in the unit is large, the total expenses paid to a and B travel agencies are the same
(2) If there are 30 people in the unit participating in the tour, which travel agency should you choose to reduce the total cost?
(1) Equality relation: the total expenses paid to a and B travel agencies are the same
Suppose that when the number of tourists in the unit is x, the total expenses paid to a and B travel agencies are the same
300 × 75% X Yuan to travel agency a and 300 × 80% (x-1) yuan to travel agency B
(2) A: 300 × 30 × 75% B:
8. A group of infantry advance at the speed of 5.4 km / h. It takes 10 minutes for the correspondent to ride from the end of the team to the head of the team and immediately return to the end of the team. If the speed of the correspondent is 21.6 km / h, what is the length of the infantry queue?
Equal relation: time from correspondent to the head of the team + time from correspondent to the end of the team = 10 minutes
Suppose the length of infantry formation is kilometer (the unit should be unified)
From the end of the team to the head of the team in the same direction: the length of the team △ the speed difference; from the head of the team to the end of the team in the opposite direction △ the speed sum
The answer process should be complete
9. There are 32 people in team a and 28 people in team B. if some people are transferred from team B to team a, the number of team a is just twice that of team B. how many people are transferred from team B to team a?
Equivalency: after transfer, the number of team a is exactly twice that of team B
Suppose that x people are transferred from team B to team a, and the remaining number of team B × 2 = the number of team a
The answer process should be complete
10. The distance between a and B is 1.8 ㎞. A and B start from a and B at the same time and walk towards each other. A rides a bicycle at a speed of 12 ㎞ / h, and B walks. After 6 minutes, they meet to find the speed of B
Equal relation: meeting shows that two people have left. A and B are far away. A + B = A and B are far away
11. A passenger train is 200 meters long and a freight train is 280 meters long. They run in parallel tracks. After 18 seconds from meeting to leaving at the end of the train, the speed ratio of the passenger train to the freight train is 5:3. How many meters do the two cars run in each second?
But the length of the line is the sum of the length of the two trains
Long sum of two trains △ speed sum = 18 seconds
12. A plane flies between the two cities with a wind speed of 24 km / h. It takes 2 hours and 50 minutes to fly along the wind and 3 hours to fly against the wind. Find the distance between the two cities
Equality relation: given time, speed can be set, which means distance between two cities = distance between two cities
(distance between two cities = speed (static speed + wind speed) × time, downwind)
Distance between two cities = speed (static speed wind speed) × time (headwind)
13. A circular runway is 400 meters long, a 550 meters per minute, B 250 meters per minute
(1) A and B set out in opposite directions at the same time. How many minutes will they meet again?
(2) A and B set out in the same direction at the same time. How many minutes will they meet again?
Equal relationship: (1) the circle runway starts in the opposite direction, and the sum of the distance run by two people is equal to the length of the runway
Let's say they meet again in X minutes
(2) The distance difference between the two runners is equal to the length of the track
Let's say they meet again in X minutes
The answer process should be complete
14. There are two charging methods for mobile phone charge cards, as shown in the table below:
Global card China card
The monthly rent is 50.00 yuan / month and 0.00 yuan / month
Call fee 0.40 yuan / min 0.60 yuan / min
If your parents buy a mobile phone, how do you choose a mobile phone card for your parents?
(similar to 7) depending on the length of use, find a point where the cost is equal, and then choose
Equal relationship: Global card fee = China card fee
Let the cost of using X minutes be equal
Global pass card fee: (50 + 0.4x) yuan, Shenzhou bank card fee: 0.6x yuan
15. The speed of a local train is 48 km / h, and that of an express train is 55 km / h. The distance between the two workshops is 21 km. How many hours does it take for the express train to catch up with the local train at the same time?
Equal relation: the distance of fast train - the distance of slow train = the distance between two workshops
16. In order to encourage citizens to save water, a city has made the following provisions:
Water charge
No more than 10 m3 0.5 yuan / m3
1.00 yuan / m3 for each additional 1 m3 above 10 m3
Xiao Ming's family paid 20 yuan for water in September. How much water did his family use in September?
Equality relation