First of all, a brief introduction.

There are three formulas to solve engineering problems: working efficiency × working time = total work, total work difference ÷ working efficiency difference = working time, total work sum ÷ working efficiency sum = working time; Engineering problems are generally divided into two situations, one is to know the total workload, and the other is to find the total workload.

Second, classification

1. There are two problems when the total workload is known: the specific amount of the total workload is known. Students often solve this problem smoothly. Because all the conditions are intuitive, you only need to understand the meaning of the question to import the formula; Although the specific amount of the total work is unknown, we can assume that it is the "first unit". In this case, the working hours are often known.

2. In the second case, the total workload is unknown. This kind of problem is very simple, and it is generally known that work efficiency and working hours.

Third, engineering problems.

1. Engineering problem is the focus of mathematics application problem teaching in primary and secondary schools, the extension and supplement of fractional application problem, and an important tool to cultivate students' logical thinking ability. It is a powerful penetration of the idea of one-to-one correspondence of functions in application problems. The engineering problem is also the difficulty of the textbook.

2. The engineering problem is an application problem that regards the total workload as the unit "1", which is abstract and difficult for students to identify. In teaching, how to make students establish correct concepts is the key to mathematical application problems. This lesson runs through the concept of engineering problems, aiming at making students understand and master the concepts skillfully.

3. Contact the actual conversation. Introduce the concepts of suspension and infiltration. The purpose is to let students review and understand the concepts of total workload, working hours and work efficiency and their quantitative relations. The initial evaluation once again strengthened the concept of engineering problems. By comparison, the concept is established.

4. Give full play to students' dominant position in teaching, and use students' existing knowledge to solve cooperation problems. Rational use of reinforcement concept. On the basis of perception, students initially form the representation of the concept in their minds and have the prototype of the concept. Some students just accepted this concept and haven't fully digested it.