1, we need to know the working principle of electric fans. The switch of the electric fan is a mechanical device, and every time it is pulled, it will change the internal contacts, thus changing the power state of the electric fan. Pull down the switch, the electric fan will be connected to the power supply and start to rotate; Pull again, and the electric fan will cut off the power supply and stop running.
We think there are 40 students in this class. Each student only pulls the switch once. Then, after the first student pulls the switch, the state of the electric fan lights up. When the second student pulls the switch, the state of the electric fan will be turned off because the contacts inside the switch have changed.
3. Whenever a student pulls the switch, the state of the electric fan will change according to the previous contact state. Therefore, when the 40th student pulls the switch, the state of the electric fan will be turned off. So, when the last student pulled the switch, the electric fan was turned off.
Fifth grade math problem solving skills;
1. Understand the background of the topic: First, you need to read the topic carefully to understand the mathematical concepts and problem situations involved in the topic.
2, determine the problem-solving strategy: according to the type and content of the topic, choose the appropriate problem-solving method. For example, for application problems, it is necessary to analyze the meaning of the problem first, find out the known conditions and unknown conditions, and then establish a mathematical model to solve them.
3. Establish a mathematical model: For application problems, a mathematical equation or set of equations can be established according to the meaning of the problem to solve the problem. For other questions, we can also choose appropriate mathematical models to answer according to the characteristics and requirements of the questions.
4. Calculation: Calculate according to the established mathematical model and get the result.
5. Integrate the answers: integrate the calculation results into a complete answer, and pay attention to the format and expression of the answer.
6. Note: The math problems in grade five begin to involve some complex math concepts, which require students to master basic concepts and formulas skillfully. When solving practical problems, we should carefully examine the problems, find out the known conditions and unknown conditions, and determine the ideas and methods of solving problems.