Sunshine Printing Factory has employees 150, of which 2/5 are men. Then a group of male employees came in. Now the ratio of male to female employees is 3: 2. How many male workers came in later?

Hint: In this issue, the key is to keep the number of female employees unchanged, "by static braking", that is to say, female employees have changed from 3/5( 150) to 2/5 after the change. The reason for the change in the total number of employees is that another group of male employees have come in, so we must first seek the first unit after the change.

2. Conversion unit 1

The three brothers bought a villa together, with the eldest paying 500,000 yuan, the second paying 1/2 of the total amount of the other two brothers, and the third paying 1/3 of the total amount of the other two brothers. What's the price of this villa?

Tip: In this question, the contribution of the second child is 1/2 of the total amount of the other two brothers, and the second child is1/3 of the total amount of the three brothers; Similarly, the contribution of the third brother is 1/4 of the total amount of the three brothers, and the total amount of the three brothers is 50 ÷ (1-kloc-0//3-1/4) =1.2 million yuan.

3. Find the corresponding score

1/3 of a rope was used, and 16 meters was connected, and the result exceeded the original 1/5. How long was the original rope?

Tip: You can draw a line chart, which means that the connected 16m not only fills in "used 1/3", but also "exceeds the original 1/5", that is, the corresponding score of 16m is (1/3+/.

4. Understand key sentences

Party A and Party B walk across from AB, with Party A walking 50 kilometers per hour and Party B walking 40 kilometers per hour. A few hours later, they met 30 meters from the midpoint. How many kilometers is AB?

Tip: The "meeting" in this question is not a "regular meeting". To understand that they met at a distance of 30 meters from the midpoint, it is necessary to understand that A walked 60 kilometers more than B, their speed difference was 10 km, and the meeting time was 30×2÷(50-40)=6 (hours), so the distance between the two places was solved.

5, flexible use of hypothetical strategies

It takes 5 hours to get from A to B, first uphill and then downhill. The distance between A and B is150km, the uphill speed is15km/h, and the downhill speed is 40km/h.. How many kilometers is it uphill?

Tip: It is not easy for students to think of "chickens and rabbits in the same cage" as the topic of travel. The key is to guide students to find the equivalence relationship and use the hypothetical strategy flexibly: assume that all trips are uphill, (150-5×15) ÷ (40-15) = 3. Of course, if the equivalence relation is found correctly, it will be easy to solve the problem with equations.

6. Clever use of enumeration method

Lantian Timber Factory has 56 workers. Each worker can process 10 tables or 15 square stools on average every day. In order to supply the market, 1 desks and 2 square stools must be delivered in complete sets. How to arrange the number of people processing desks and square stools so as not to cause waste and meet the supply as much as possible? (supplementary exercise, question 4 on page 72)

Tip:

Number of people, number of tables, number of chairs.

1 10 15

2 20 30

4 40 60

It is necessary to reasonably arrange the number of people processing desks and square stools, solve the problems that students are not easy to understand with comparative knowledge, and skillfully use enumeration to help students establish the appearance of division of labor: 3 people make tables, 4 people make chairs, 56÷(3+4)=8 (group), 3×8=24 (person) makes chairs: 4×8=32 (group) Of course, it is also a good choice to solve with equations.