Divide two digits into ten digits and ten digits, then multiply them by one digit respectively, and then add up the products.

Example: 12×3, 12 can be divided into 10 and 2, and then multiplied by 3 respectively, and the products are added; that is

Illustration demonstration example demonstration

Another example is: 123×3. Divide 123 into 100, 20, 3, then multiply them by 3 respectively, and then add the products, that is, 100×3=300, 20×3=60, 3×3=3.

2. Vertical calculation classification of two or three numbers multiplied by one number:

(1) Vertical calculation of multiplying two or three digits by one digit: starting from the single digit, multiply the number on each digit of two or three digits with the number on which digit in turn, and the result of multiplication will be aligned with that digit.

Legend display: sample demonstration

< Analysis > When the columns are vertical, the endpoints of the two multipliers are aligned. First multiply the number 2 and the number 4 in the 24 bits of the two-digit number, and the result 8 is written below one bit. Then multiply the number 2 by the number 2 in the 10 bit of these two digits, and the result 4 is written below these ten digits.

(2) Calculation of one round in the calculation process: ① Starting from one digit, multiply each digit of two or three digits by one digit in turn; (2) Whoever gets the best scores will be promoted to the top one (note: when calculating the top one, the result will be added with the promotion number).

Legend display: sample demonstration

< analysis > for the result of one digit and unit, 4×4= 16 goes forward (ten digits enter one) and the remaining 6 is written below the unit. For the results of one digit and ten digits, 4× 20 = 80,80+10 = 90, that is, write 9 below the ten digits.

(3) Calculation of continuous carry in the calculation process: ① Multiply one digit by the single digits of two or three digits, and when the product is dozens, advance to the previous digit (ten digits); (2) Multiply one digit by ten digits of two or three digits, and add the added number to the multiplied product. If it is dozens, it will be added to the next (hundreds); (3) Multiply a number by one percent of two or three digits, and don't forget to add the number that yields the product. If it's dozens, go to the next one.

Legend display: sample demonstration

(4) The use of 0 in the multiplier:

① Particularity of 0: Any number multiplied by 0 will get 0, or 0 multiplied by any number will get 0.

Principle: The calculation of 5×0 can be converted into the addition of five zeros, and 0+0+0 = 0, so 5×0=0, and so are other numbers.

② There is a zero at the end of the multiplier, and there are two vertical methods: it can be calculated according to the normal vertical method of two or three digits, and it can also be regarded as dozens or hundreds of columns.

Picture display: sample demonstration

③ When there is a 0 in the middle of the multiplier, the calculation method is still the same as that of two or three digits multiplied by a digit and then multiplied by a digit, for example, 204× 2 (first multiply the number 2 of a digit by the number 4 of three digits to get 8, then write the number 0 multiplied by the number 0 below the digit, and finally write the number 2 multiplied by the number 4 below the digit. )

Another example: 204× 3 () vertical formula is as follows:

Picture display: sample demonstration

3. Knowledge expansion:

(1) A mixed operation with two or three numbers multiplied by one number:

Example: Teacher Zhang took 100 yuan and went to the supermarket to buy a pencil case and a stationery bag 15 yuan. Teacher Zhang bought five. How much money does Teacher Zhang have left?

< Analysis > To solve this problem, we must first solve how much money Teacher Zhang spent (that is, how much money is needed for five pencil boxes-how much is five 15: 15×5=75, and then subtract 75 from the belt 100, and the comprehensive formula is100-.

Teacher Zhang has 25 yuan left. )

(2) Multiplication of two or three digits by one digit:

Example: A box of chocolates has 4 pieces, and one piece is sold in 2 yuan. How much is a box of 12 chocolates?

< analysis > ① You can calculate how many chocolates there are in a box of12 * *:12× 4 = 48 (blocks), and then calculate the cost of 48 pieces of chocolate: 48×2=96 (yuan). Comprehensive formula:

12×4×2=48×2=96 (yuan)

A: I need 96 yuan.

② You can also calculate the cost of a box of chocolates first: 4×2=8 yuan, and then calculate the cost of 12 box: 12×8=96 yuan. Comprehensive formula:

4×2× 12=8× 12=96 (yuan)

A: I need 96 yuan.