Is the total price in proportion to the unit price Most people think that it is in a positive proportion, but in the positive proportion relationship, it says: there are two related quantities, one of which changes with the change of the other. The unit price is not a variable quantity, but the quantity is certain. Can it still be in a positive proportion? In real life, how can the unit price change constantly?

Is the total price in proportion to the unit price Most people think that it is in a positive proportion, but in the positive proportion relationship, it says: there are two related quantities, one of which changes with the change of the other. The unit price is not a variable quantity, but the quantity is certain. Can it still be in a positive proportion? In real life, how can the unit price change constantly?

In proportion
In "two related quantities, one changes with the change of the other", the quantity that changes with the change of the other is called dependent variable, and the quantity that actively changes and causes other quantities to change with it is called independent variable
Total price = unit price × quantity
The unit price is an independent variable and the total price is a dependent variable. When the quantity is constant, the unit price as an independent variable changes, and the total price as a dependent variable naturally changes in proportion. This proportion is the quantity. If the unit price does not change, the total price will not change
In real life, the unit price changes are very normal. For example, when the market is good and the price rises, the unit price is changing. Or when the raw materials go up and the cost goes up, the unit price will also change. There are also promotions and discounts. In essence, the unit price is changing

Check whether the two quantities in the following question are in a positive proportion. (mark √ for the positive proportion, and X for the negative one.)
(2) Zhang Xiang's height and age
(3) Total price and number of copies of China Youth Daily
(4) Perimeter and side length of a square
(5) The yield of wheat per hectare is fixed. The total yield is the same as the number of hectare of wheat planting
(6) The work efficiency is constant, the total amount of work and working hours
(7) Area and radius of a circle

1) Positive proportion
2) Out of proportion
3) Positive proportion
4) Positive proportion
5) Positive proportion
6) Positive proportion
7) Not in proportion

If the quantity is fixed, is the unit price proportional to the total price?

Yes, in line with the definition of positive proportional relationship
Positive proportional relationship refers to:
If the ratio of two numbers corresponding to two dependent variables is constant, the two variables are called positive proportional variables, and their relationship is called positive proportional relationship

If the unit price of apples is fixed, is the quantity of apples in direct proportion to the total price? Is the radius of a circle in direct proportion to its area? Explain the reason
Write a specific blackboard writing process

If the unit price of apples is fixed, is the quantity of apples in direct proportion to the total price;
It's in direct proportion
Because: total price = unit price * quantity
Is the radius of a circle proportional to its area? Explain why
Out of proportion
Because: area = Pai * radius * radius