Note: For example, the length of the first painting is twice the width, which can also be expressed as: the aspect ratio is 2: 1, marked as 2: 1, and ":"is a tick. The width is 1/2, which can also be expressed as: the width-length ratio is 1: 2. Excuse me, how to express the length-width relationship between the second picture and the third picture by ratio?
Students use ratio to show the relationship between the length and width of the other two pictures.
Teaching objectives:
1. Understand the significance of ratio in specific situations, learn to read and write ratio, and master the names of each part of ratio and the method of finding ratio.
2. Experience the process of exploring the relationship between ratio, fraction and division, understand the internal relationship between mathematical knowledge, and grasp the essence of the meaning of ratio.
3. In autonomous learning, accumulate experience in mathematics activities, cultivate students' ability to analyze and summarize, and feel the fun of mathematics learning.
Ratio of the same amount:
Teacher: Just now we used "15÷ 10" to indicate how many times the length is the width. It can be said that the length-width ratio is 15 to 10, and it is recorded as 15: 10. Then, 10÷ 15 means that the width is a fraction of the length. How to express their relationship by proportion? (It can be said that the aspect ratio is 10 to 15, and it is recorded as 10: 15. )
Teacher: Think about it. 15 is the same as 10 or 10? What's the difference between them? Guide the students to understand that the former and the latter have different meanings. )