Secondly, we should know what ratio is: the division of two numbers is called the ratio of two numbers.
In addition, we should understand what the unit is 1: the unit 1 can represent the number 1, but it is more important to represent an object, a unit, a whole, a part and so on in fractions, percentages, engineering problems and so on. For example, the unit 1 can represent: a pile of apples, a box of chalk, the number of people in a class, one month.
All units of 1 are called standard quantities, and those compared with units of 1 are called comparative quantities.
When solving application problems, if the quantity of unit 1 is known, then multiply the known quantity by the proportion corresponding to the required quantity to get the comparative quantity; On the contrary, if the comparison amount is known, the amount of unit 1 can be obtained by using the ratio of the comparison amount to the comparison amount. Therefore, the selection of 1 unit is very important. As long as you choose the unit 1, you can know the calculation method.
Regarding how to choose the unit of 1, the whole is generally chosen as the unit of 1, but some topics are similar comparisons. Choosing which unit of 1 is very important for the simplicity of calculation, and this kind of topic needs more practice and thinking.
For example, what percentage of 5 is 4? What percentage of this question is 4: 5? Here we only need to take 5 as the unit 1 (here the unit 1 is 100), that is, we can know what percentage is 4 times 100. Because of this ratio, the first and last terms of the ratio are multiplied or divided by 1 at the same time.
When learning this knowledge point, we should also understand that there are many similarities between ratio and division and fraction, and we should learn to integrate the knowledge of division, ratio and fraction.