1

Because the (unit price) of ballpoint pens is fixed, the total price changes with the change of (quantity). With the increase of the number of branches, the total price (also increases); When the number of branches decreases, the total price also decreases, and the ratio of the total price to the number of branches is certain, so we say that the number of branches is directly proportional to the total price.

2

Speed × time = distance

When the ratio is constant, the speed is proportional to the hand time; When the quotient is constant, distance is proportional to time.

(I don't want to answer next, please forgive me ~)

p25

1

Because the total price is fixed, the number of bottles changes with the change of unit price.

As the unit price increases, the number of bottles decreases.

When the unit price decreases, the number of bottles increases, and the product of the unit price and the number of bottles is certain.

We say that the unit price is inversely proportional to the number of bottles.

2

The relevant quantities are speed and time.

The speed varies with time.

The distance is certain.

therefore

Speed is inversely proportional to time.

two

1 What are the two quantities in the table? Are they related quantities?

200×300=300×20=400× 15=500× 12=6000

Answer: There are two quantities: the number of kilograms you eat every day and the number of days you can eat. They are related quantities.

2. Write several groups of products of two numbers corresponding to these two quantities and compare the sizes.

200×30=6000

300×20=6000

400× 15=6000

6000=6000=6000

Are the two related quantities in the table inversely proportional? Why?

Answer: It is inversely proportional, because the product of the number of kilograms you eat every day and the number of days you can eat is certain.

three

1. A: These two numbers are not inversely proportional, because the total number of pages in a book = the number of pages read+the number of pages left, the sum is certain, and the difference is also certain.

2. Answer: These two figures are inversely proportional, because the total number of units (certain) = the number of units produced every day × the number of days.

3. These two numbers are inversely proportional, because base × height = area of parallelogram (certain).

four

1.

2.x

0. 1

0.2

0.4

0.5

y

40

20

10

eight

A: xy is directly proportional.