The oral calculation method of (1) multiplying two digits by one digit (carry): first divide the two digits into one (integer ten) and one (one digit), then multiply them with one digit respectively, and finally add the products of the two multiplications.
(2) Method of multiplying two-digit numbers by integer 10 and integer 100 (no carry): multiply the numbers before (0) first, and then see how many (0) are at the end of the two multipliers, and add several (0) at the end of the product.
Exploration algorithm:
1, teach an integer ten times a digit.
Teacher: Please look at this picture carefully. What mathematical information can you find? What would you do if you were given a chance to play? Xiaohong wants to play bumper cars with her parents. Can you ask a math question? Tell the whole question.
(1) Guide students to ask math questions, such as: How much does it cost for three people to go to 20 yuan by bumper car?
(2) What do you know through reading and reviewing the questions? Ask for what?
(3) How to make it? 20×3=60 (yuan).
(4) Why use multiplication? Student: 20 yuan per person, three people need three 20 yuan, so we use multiplication.
(5) How did this 60 come from?
2. Group cooperative learning: how to calculate 20×3? Talk and write down your thoughts in the group.
(1) cooperative learning.
(2) Report:
A, waving a stick: 3 bundles of two is 6 bundles, which is 60.
20+20+20=60 .
C, two tens times three is six tens, which is 60.
D, first calculate 2 times 3 to get 6, and then add a 0 after 6.
Teacher: The students are really nice. They have come up with so many good ideas. Which one do you like best?
(3) Now that you have learned that 20×3=60, can you count it as 200×3? What about 20xx×3?
(4) Look at these three formulas carefully. What do they have in common?
Student: One multiplier is a single digit, and the other multiplier is an integer ten, an integer hundred and an integer thousand.
Teacher: This is what we are going to learn today, "Whole ten, whole hundred, whole thousand times one digit".