Maximum product: 930×87=809 10 or 870× 93 = 80910;

Minimum product: 789×30=23670.

According to the knowledge of multiplication, when two factors are large, their products are also large; When these two factors are small, their products are also small. Comparing 930×87=809 10, 870×93=809 10 and 970×83=805 10, we can see that 930×87=809 10 and 870× 90. Minimum 789×30=23670.

increase

Multiplication is a shortcut to add up the same numbers. The result of its operation is called product, and "X" is the symbol of multiplication. From the philosophical point of view, multiplication is the result of qualitative change caused by additive quantity. The multiplication of integers (including negative numbers), rational numbers (fractions) and real numbers is a systematic summary of this basic definition.

Multiplication can also be seen as calculating the objects arranged in a rectangle (integer) or finding the area of a rectangle with a given side length. The area of the rectangle does not depend on which side is measured first, which shows the exchange property. The product of two measured values is a new type of measurement, for example, multiplying the length of two sides of a rectangle to get its area, which is the theme of size analysis.

In the process of arithmetic development of various civilizations, the generation of multiplication operation is a very important step. A civilization can successfully develop counting methods and addition and subtraction operations, but it is not so easy to create simple and feasible multiplication methods.

The vertical calculation of multiplication seems simple, but it is necessary to master the formula table of 99 multiplication in advance; Considering this, this vertical calculation is not perfect. It will soon be seen that in the development of mathematics, different civilizations have created different multiplication methods, and some can even abandon the multiplication table completely.