Knowledge points:

A, oral multiplication:

Multiply the integer 10 with the integer 100, and then multiply the numbers before 0, and then see how many zeros are at the end of the two factors, and add a few zeros at the end of the product.

For example: 30×500= 15000? You can think of it this way: 3×5= 15, and there are three zeros at the end of a * * * of two factors. Add three zeros after the result 15 to get 30× 500 = 15000.

Second, the estimate:

By multiplying a two-digit number by a two-digit number, you can treat the factor as an integer ten first, and then calculate it. (One factor can be regarded as a divisor, or two factors can be regarded as a divisor at the same time. )

Such as: 22× 18≈400? Or? 22× 18≈360 ? Or? 22× 18≈440

Third, the pen multiplication:

① Multiply the first factor by the number of digits of the second factor, and the end of the number is aligned with the number of digits of the first factor.

② Multiply the first factor by the ten digits of the second factor, and the end of the result is aligned with the ten digits of the first factor.

(3) Then add up the products of the two times.

Fourth, a friendly reminder:

1, the product of two digits multiplied by two digits may be (3) digits or (4) digits.

2. Checking calculation: exchange the positions of two factors.

3. When solving practical problems, make a reasonable estimate according to the actual situation.

4, column calculation, must list the comprehensive formula, from the calculation.

5. Multiplication of several special numbers (remember): 25×4= 100, 125×8= 1000.

6. Correlation formula: factor × factor = product? Product display coefficient = another coefficient