1. When three digits are multiplied by two digits, multiply three digits by two digits first, and then multiply three digits by ten digits of two digits.

Number to multiply this three-digit number. Finally, add up their products. ?

2. Multiply with 0 at the end of the factor: when writing vertically, align the numbers before 0 and multiply only the numbers before 0; How many are there at the end of two factors?

0, just add a few zeros at the end of the product. ?

3. Law of product change:?

(1) If one factor remains unchanged, another factor will be expanded (or reduced) several times, and the product will be expanded (or reduced) by the same multiple. ?

For example, 1: It is known that A×B=2 15, then A×B×2= (). ?

This is to expand B by 2 times, and the product will also be expanded by 2 times. That is, 2 15×2=430, so A×B×2=(430). ?

For example, 2: known: 2×A×B=200, then A×B= (). ?

In this way, a is reduced by 2 times and the product is also reduced by 2 times. That is 200÷2= 100, so A×B=( 100). ?

(2) One factor is expanded or reduced by several times, and the other factor is reduced or expanded by the same multiple, and the product remains unchanged. ?

For example, A×B=5 10 is known. If A is enlarged by 5 times and B is reduced by 5 times, the product is (5 10). ?

(3) If one factor is expanded m times and the other factor is expanded n times, the product is expanded m×n times. ?

④ If one factor is reduced by m times and the other factor is reduced by n times, the product will be reduced by m×n times. ?

(4) One factor is expanded by m times and the other factor is reduced by n times. If m >；; N expands the product by (m÷n) times. If m

6. Speed × time = distance/time = speed/distance/speed = time

Unit price × quantity = total price ÷ total price ÷ quantity = unit price ÷ total price ÷ unit price = quantity