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通用小学数学教材第四册第55页14题:“小明今年8岁,他的父亲38岁。小明多少岁的时候,他父亲的年龄正好是他的2倍?”该册教学参考书第32页写道:“这道题可以这样解答:38-8=30,当小明30岁时,他父亲的年龄正好是他的2倍。”我认为这样列式人们容易误解。因为算式38-8=30所表达的意义是:父亲与儿子小明现在的年龄之差,也是他们任何时候的年龄差。由于父亲的年龄是小明的年龄的2倍时,这个年龄差恰好是小明这时的年龄的(2-1)倍,所以算式应为:(38-8)÷(2-1)=30(岁)。
14: “Xiao Ming is 8 years old this year and his father is 38. How old is Xiao Ming, his father's age is exactly 2 times his age?” The book teaching reference book 32 Page wrote: “This question can be answered: 38-8 = 30, when Xiaoming is 30 years old, his father's age is exactly 2 times his age.” I think such formula is easy to misunderstand. Because the expression 38-8 = 30 is the meaning expressed by the difference between the present age of father and son Xiaoming and the age difference of any time. Since the age of the father is twice the age of the Xiao Ming, the age difference is exactly (2-1) times the age of the Xiao Ming, so the formula should be: (38-8) ÷ (2-1) = 30 ( year old).