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"Three Numbers Divided by Two Numbers" in Primary Mathematics

First, review the test questions

Note: The picture is taken from page 69 of the first volume of Mathematics for the Fourth Grade in Primary School published by Beijing Normal University Press.

Second, the analysis of test questions

teaching process

(A) the introduction of new courses

Group representatives share, teachers guide and improve business trial methods;

Firstly, determine how many digits the quotient is, and look at the first two digits of the dividend and the first two digits of the divisor;

Secondly, the divisor is regarded as an integer close to it by rounding, and the quotient is tried by multiplication formula.

Special analysis of national defense

1. Talk about your views on the trial operation method.

Reference answer

The whole calculation step is added in the process of business test, and sometimes the quotient needs to be adjusted. It may take several attempts to succeed, which tests the patience of students. Secondly, it is easy to make mistakes when trying to decide which quotient should be written, and students need to master arithmetic to facilitate calculation.

Trial quotient should first understand that the first two digits of dividend are not enough to divide, and look at the first three digits. Secondly, what can be used to divide the divisor in this class with two digits? Rounding? Method, such as 154? 22, you can turn 22 four rooms into 20 for trial business; And 120? 18 can be divided into five parts for trial quotient; All these can be tried in one step, but some can't be successful at one time, such as 185? 37, take 37 as 40 test quotient, the initial quotient 4 is too small, and then change it to quotient 5. Therefore, if the trial trader adopts the Fourth Institute, the initial chamber of commerce will be too large and should be adjusted downward; Input 5 is easy to be too small, so it should be increased. Finally, check the results.

2. What role does this class play in the whole process of primary school mathematics teaching?

Reference answer

This lesson mainly teaches the mathematical knowledge of dividing three digits by two digits (non-integer ten digits), which is the key stage of integer division in primary school mathematics and plays a connecting role. The focus of this lesson is to teach the written calculation of dividing three digits by two digits (not integer ten digits). By trying the commercial law, we first estimate and then get the accurate result. The ability of trial quotient will directly affect the speed and correctness of division calculation, and this part of knowledge will also lay the foundation for subsequent calculation.