This topic examines the related knowledge of inequality, enumerates inequality equations, solves inequality equations and the properties of inequality. Cultivate the ability to analyze and solve problems, and turn practical problems into mathematical problems.

Thinking of solving problems: column inequalities are the same as equations. To find the core relationship, this problem can be formulated with time or distance as the core. The distance should be greater than 100 m; The time should be that the fuse blows more than the time for people to escape.

Specific problem-solving process: If the fuse length is x(cm), the fuse blowing time is x/0.5(s), and the distance people run is x/0.5(s)X4cm/s=8x(cm). And the escape distance should be greater than 100m= 10000cm. Therefore, inequality should be:

8x & gt 10000

If arranged in chronological order, it should be:

x/0.5 & gt； 10000/4

Summary of this topic: Because it is an exercise for seventh-grade students, we should pay attention to the understanding and application of basic knowledge. Combined with students' previous knowledge accumulation, the main direction is to gradually cultivate the ability to analyze and solve problems, and to explain and solve simple problems in detail.