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本段教材的主要目的是:使学生会用小数乘以整数的计算方法,并能运用它来解答应用题。教材开始是计算被乘数是一位小数,乘数是一位整数的问题,接着是计算被乘数是两位小数,乘数是一位整数的问题,再出现了用两位小数乘以两位整数的应用题,及带小数乘以三位整数的计算问题,逐步巩固、扩大已获得的知识,并使学生知道乘积小数末尾的零,根据小数聚法,要把它消去。计算这些题的原理是:把被乘数扩大10倍(或100倍),使它变成整数,依照整数乘法的计算方法算出乘积,再概据“因数的变化而引起积的变化”的关系将乘得的积,相应地缩小同样的倍数,即为原有的积。通过以上各题的计算,得出小数乘以整数的计算方法:先把被乘数当做整数来进行计算,然后把得出的积加上小数点,被乘数有几位小数,积也有几位小数。并运用“把小数改成分数,以分数乘以整数”的算法,来验证上述小数乘以整数的法则所得结果的正确性。本段教材可以分为两个课时进行。
The main purpose of this textbook is to enable students to multiply an integer by a decimal number and to use it to answer questions. The beginning of the textbook is to calculate the multiplicand is a decimal, the multiplier is an integer, followed by the calculation of the multiplicand is two decimal places, the multiplier is an integer, and then appeared with two decimal multiplied The application of two integers, and the calculation of fractions with decimals and three integers, gradually consolidate and expand the knowledge gained and enable students to know the zero at the end of the product decimal, which should be eliminated according to the decimal aggregation method. The principle of calculating these questions is to multiply the multiplicand by a factor of 10 (or 100) so that it becomes an integer, and then calculate the product in accordance with the calculation method of integer multiplication, and then estimate the relationship between the product change caused by the change of the factor Will be multiplied by the product, corresponding to reduce the same multiple, is the original product. Through the calculation of the above questions, come to calculate the decimal multiplied by an integer: the multiplicand as an integer to be calculated, and then add the product of the decimal point, the multiplicand has a few decimal places, there are a few product Decimal And use the “change the decimal fraction to the fraction multiplied by the integer” algorithm to verify the correctness of the result of the above decimal number multiplied by an integer. This section teaching materials can be divided into two hours.