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When a boat finds a leak, it has entered some water, and the water enters the boat at a constant speed. If 10 people clean the water, it will finish in 3 hours; if 5 people clean the water, it will finish in 8 hours. If it is required to finish in 2 hours, it should be arranged___ A man washes for water
Suppose that the amount of water washed out by one person in one hour is 1, the total amount of water in three hours is 10 × 3 = 308, the total amount of water in three hours is 5 × 8 = 40, the water inflow in one hour is (40-30) / (8-3) = the total amount of water in 22 hours is 30-2 = 28, the number of people needed is 28 △ 2 △ 1 = 14, so the answer is: 14
A job, a alone 12 days to complete, B alone 8 days to complete, now two people cooperate, midway a rest 2 days, B did not rest, complete this work share how many days?
(1-18 × 2) △ 112 + 18 + 2, = 34 △ 448 + 648 + 2, = 34 △ 524 + 2, = 3.6 + 2, = 5.6 (days); a: it takes 5.6 days to complete the work
How to solve the engineering problems of grade six in primary school
Engineering problem is an important type of applied problems in primary school, and it is also a key and difficult point in the applied problems of primary school scores. The quantitative relationship of this type of applied problems is relatively hidden, and sometimes it is complicated to use the usual methods to solve them. If we use special methods to analyze and think, we can turn the difficult into the easy, The purpose of this paper is to make students master the rules and skills of solving engineering problems
1、 Answer with unit "1"
[example 1] for a project, team a does it for 12 days and team B does it for 20 days. How many days does it take for the two teams to work together?
[analysis] take the total amount of the project as unit "1". Team a completes 1 / 12 of the project in one day; Team B completes 1 / 20 of the project in one day; team a and team B jointly complete 2 / 15 of the project in one day. The number of 2 / 15 included in the total amount of work "1" is the number of days for the two teams to complete the project
1 ÷ (1 / 12 + 1 / 20) = 7.5 (days)
[comment] this is the basic problem of an engineering problem. Take the total amount of work as a unit of "1", divide the total amount of work by the sum of work efficiency, and you can calculate the time to complete the project
2、 Answer with copies
[example 2] for a project, it takes 12 days for Party A to do it alone, and 15 days for Party B to do it alone. Now Party A has done it alone for 3 days, and Party B has joined in to do it together. How many days will it take to complete it?
[analysis] the total amount of the project is divided into (12 × 15) parts. It takes 12 and 15 days for Party A and Party B to complete the project alone. It is known that Party A and Party B can complete 15 and 12 parts of the project respectively every day, and can make (15 + 12) parts together every day. Party A has done (15 × 3) parts for 3 days, and the rest is (12 × 15-15 × 3). The time required for Party B to join in the project is: (12 × 15-15 × 3) / (15 + 12) = 5 (days)
When solving this kind of practical problem, the key is to regard the product of the time required by a and B as the total number of shares
3、 Answer with multiple relation
[example 3] a batch of parts is processed by the master in 14 days. If the master and the apprentice work together for 10 days, how many days does it take for the apprentice to work alone?
[analysis] the master did it for 10 days + the apprentice did it for 10 days to complete all the work;
The master does all the work in 14 days (10 days + 4 days). From this, we can see that the workload of the master in 4 days = the workload of the apprentice in 10 days, that is, the work efficiency of the master is 2.5 times that of the apprentice, so the apprentice alone needs 14 × 2.5 = 35 days
[comment] in solving this problem, the work efficiency of master is 2.5 times that of the apprentice, so the number of days required for the apprentice to do it alone can be simply calculated
RELATED INFORMATIONS
- 1. If a work is done alone, Party A can complete it two days ahead of schedule. Party B can complete it three days ahead of schedule. Now, after two days of cooperation, Party B will continue to do the rest alone, just in time. If cooperation, how many days will it take to complete the project?
- 2. For a project, Party A and Party B work together for 20 days, and Party A has worked together for 2 days after 3 days to complete 1 / 5 of the whole project. How many days does it take for Party A and Party B to work alone? Remember, ”Three days later, it was followed by "three days later, B followed". Just understand.
- 3. For a project, Party A will do it alone in 15 days and Party B will do it alone in 20 days. After three days of cooperation between the two teams, team B will do the rest of the project alone. How many more days will it take to complete? -------------------------------------------------------------------- Please send the formula and solution to me if you know the answer,
- 4. Several simple primary school mathematics calculation problems What can be calculated simply should be calculated simply: 11.58-（5/11+1.58） 24*（1/3+8/3+7/12） 120.8*3/4-0.8*3/4 99 * 97 / 98 thank you {(this symbol means multiplication *) (/ followed by denominator)
- 5. Non application questions on prime numbers Fill in the appropriate prime number in the brackets to make the formula true! 98=(）X（）x（） 100＝（）x（）x（）x（）x（） 110＝（）x（）x（） 112＝（）x（）x（）x（）x（） 114＝（）x（）x（）x（）
- 6. 1. A section of road AB is 240 meters long. A starts from a to B. half an hour later, B starts from B to a at the speed of 36 km / h. When a and B meet, the time ratio of a and B is 6:5, 2. The price ratio of a and B is 7:3. After the price rises by 70 yuan, the price ratio is 7:4. How much is the original price of a and B? 3. There are two kinds of apples, the price ratio is 5:4 and the weight ratio is 2:3. After mixing the two kinds of apples into 100kg, the unit price is 4.4 yuan per kg. How much is the original unit price? It's better to solve it by arithmetic
- 7. Seek master solution elementary school mathematics application problem ~! Urgent~~~~~~ Lele drinks a glass of milk in four times. For the first time, he drinks 1 / 5 of a glass, and then fills it with water. For the second time, he drinks 1 / 4 of a glass, and then fills it with water. For the third time, he drinks 1 / 2 of a glass, and then fills it with water. For the fourth time, he drinks it all in one gulp. Does Lele drink more milk or more water
- 8. In a hurry! Answer in half an hour! Elementary school mathematics sixth grade score application problem! There are two piles of coal a and B. pile a is 120 tons more than pile B. If 25 tons are transported from pile B to pile a, the weight ratio of pile AB is 5:3. How many tons of coal are there in pile a and pile B?
- 9. How about the distance and pursuit in the fifth grade of primary school? 1. A and B start from a certain place at the same time and travel in the same direction. A's speed is 12 kilometers per hour, which is 3 kilometers slower than B's. it takes 0.25 hours for B to repair the car on the way. When B catches up with a, how many hours did a ride? 2. The apprentice makes 8 parts per hour, and the master makes 14 parts per hour. The apprentice makes 24 parts first, and then the master starts to process them. How many hours after the master makes them, do they make the same parts? 3. They worked 8 hours. The apprentice made 8 pieces per hour, and the master took 3 hours to repair the machine. After work, the master made 11 more than the apprentice. How many pieces per hour does the master process?
- 10. Sitting on a moving train, Xiao Ming saw from the window that it took 6 seconds for the oncoming truck to pass, and the truck was known to be 168 meters long. Later, he saw from the window that it took 12 seconds for the train to pass a 180 meter long bridge______ Kilometers
- 11. Randomly investigate the birthdays of 100 people (including the elderly, young and middle-aged, children, etc.), and find out the probability that two of them have the same birthday (can be different years)
- 12. What is the probability that at least two people born in March will have the same birthday? A（30×29）/31² B 1-（30×29）/31² C 1/31 D 2/31
- 13. The probability of two out of 50 having the same birthday 365 days
- 14. What is the probability that at least two of n people have the same birthday?
- 15. 1. There is a chain made of red, white and black beads in the order of five red, four white and three black beads, sharing 185 beads. How many are the black beads? What color is the 69th?
- 16. What are the wide angles of mathematics from the second volume of the first grade to the second volume of the sixth grade of PEP? Write clearly!
- 17. Wide angle mathematical problems in sixth grade mathematics 1. For any seven different natural numbers, the difference between at least two of them is a multiple of 6. Why? 2. In 1,2,3,..., 49,50, at least how many different numbers must be taken out to ensure that one of them can be divided by 5? 3. There are 63 students in a class. They all participate in extracurricular interest groups. The activities include mathematics, art, calligraphy and English. Each student can participate in one, two, three or four interest groups. How many students in the class participate in the same project? 4. Give 400 cards to several students, each of whom can get no more than 11 cards. Try to prove that at least 7 students get the same number of cards How many questions can I answer? I'm in a hurry. I'm in a hurry. I'm in a hurry. I'm in a hurry
- 18. ① Eight chickens and 15 rabbits have () feet ② () chicken and 6 rabbits have 36 feet ③ The chicken and the rabbit have 48 feet ④ How many rabbits and chickens are there in the cage,
- 19. On the Inner Mongolia prairie, there are a group of herdsmen driving a group of cattle and sheep, people and cattle. There are 27 sheep and 100 legs at the same time. How to calculate the number of people, cattle and sheep
- 20. Practical problems in grade four of primary school The two cars left from the two places at the same time and met them two hours later. At this time, they were 20 kilometers away from the midpoint of the two places. It is known that car B travels 60 kilometers per hour and car a how many kilometers per hour