The third unit of the fourth grade next semester is "Algorithm and Simple Calculation". It combines the law of addition with the law of multiplication. After students learn the law of addition, they learn the law of multiplication, which is conducive to the transfer of knowledge and easier for students to understand. In the simple calculation part, in addition to the application of "addition, subtraction, multiplication and division", the simple calculation of addition, subtraction, multiplication and division is also arranged. It can be said that simple calculation methods have appeared in this book. How to make students master these simple operations and use them comprehensively is the primary problem that every teacher thinks about. In teaching, I think we should grasp the following aspects:

First, learn to find the characteristics of the topic.

(1) When you see the numbers 5, 25 and 125, you will think of the numbers 2, 4 and 8. Multiply them to get an integer.

For example: 25, 36, write 36 as 4×9. It becomes 25×4×9, so the calculation is simple.

(2) Write an integer close to an integer and add or subtract one digit.

For example: 202×32, write 202 as 200+2 and change it to 200× 32+2× 32, and the calculation will be simple.

(3) Find out the numbers that can form an integer, and add and subtract.

For example: 126× 5+5× 74, if 126+74 = 200, we can use the multiplicative distribution law, 5×200, so the calculation is simple.

For example: 357-64-57, it is found that both 357 and 57 have a 57, and the subtraction is just an integer. We can simplify the calculation by moving numbers: 357-57-64.

Second, clever use of simple calculations.

The purpose of the simple method is to use integers to participate in the calculation, which makes the calculation difficult. The simple calculation of the topic is ever-changing, mainly to let students understand and choose simple calculation flexibly according to the characteristics of the topic.

For example, the calculation method of 28×25 can be (a) (20+8 )× 25 = 20× 25+8× 25 (b) (7× 4 )× 25 = 7× (4× 25) (c) 28× (100 ÷.

Third, pay attention to the comparison of topics.

Some students give 10 questions for simple calculation, but they may be wrong when they do it. One reason why it is difficult for students to master simple calculation is that they confuse the topic, so they don't know which simple calculation to use for the topic. In teaching, teachers should strengthen the comparison between similar topics.

For example, when comparing (25×20)×4 with (25+20 )× 4, the former uses the multiplicative associative law and the latter uses the multiplicative distributive law.

For example, compare 125×88 and 88× 102, the former is 88, 88 is 8× 1 1 or 88 is 80+8, the latter is 102, and 102 is 60.

In short, teaching should provide students with various ways of inquiry according to the characteristics of teaching content, so as to stimulate students' independent consciousness, awaken students' desire for knowledge, and urge students to update, deepen, break through and surpass their own knowledge.

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