苏教版教材四年级下册第一单元“三位数乘两位数”练习一中有这样一道思考题:用1、2、3、4、5这五个数字组成一个两位数和一个三位数。要使乘积最大,应该是哪两个数?要使乘积最小呢?换五个数字再试一试。教参中建议,本道题可以帮助学生体会两个数相乘积的大小与乘数大小的关系,但思考有一定难度,需要引导学生在分析、比较、实验和调整的过程中逐步获得结论。同时给出思考过程:要使乘积最大,两个乘数最高位上应该分别是4和5,而三位数的十位应该是3或2;因为3×5>3×4,2×5>2×4,所以两位数十位上应该是 Sujiao version of the textbook of the fourth grade under the first unit “Three figures by two figures ” There is such a practice question in question: the 1,2,3,4,5 these five figures form a two-digit And a three-digit number. Which of the two numbers should be used to maximize the product? To minimize the product, try five more digits. Teaching suggestions suggested that this question can help students understand the relationship between the size of the multiplication product multiplied by the two numbers, but thinking of a certain degree of difficulty, the need to guide students in the process of analysis, comparison, experiment and adjustment gradually get conclusions. Also given the thinking process: To maximize the product, the two multipliers should be 4 and 5 respectively, while the three digit tens should be 3 or 2; because 3 × 5> 3 × 4, 2 × 5 > 2 × 4, so the two digit tens should be