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例某粮店运来面粉和大米共4800千克,已知面粉是大米的20%,后来又运来一批面粉。这时面粉与大米的比是3:8。问又运来面粉多少千克?这道题趣味性强,综合性大,解题途径广,在教学中可指导学生用以下方法进行思考求解:[解一]用倍比法解由题意知,原来面粉是大米的20%即面粉占总重量的1/6,而面粉前后的重量分别是大米的20%、3/8,故现在面粉是原来的(3/8÷20%)倍,减去原来面粉的重量(即为1倍数),剩下部分就是又运来面粉的重量。即:4800×1/6×(3/8÷20%-1)=700(千克)[解二]用对应法解因为现在面粉和大米的总重量可以看作原来的4800千克与又运来一批面粉的和,所以现在面粉的重量相当于4800千克的1/6与
For example, a grain store shipped 4800 kg of flour and rice. It is known that flour is 20% of rice and later shipped to a group of flour. At this time, the ratio of flour to rice is 3: 8. Asked how many kilograms of flour shipped? This topic is interesting, comprehensive, wide range of problem solving, teaching in the guidance of students can use the following methods to solve: [Solutions] , The original flour is 20% of the rice flour that is 1/6 of the total weight, and the weight before and after the flour are 20% of the rice, 3/8, so now the flour is the original (3/8 ÷ 20% Subtracting the weight of the original flour (ie, multiples of 1), the rest is the weight of the flour again. That is: 4800 × 1/6 × (3/8 ÷ 20% -1) = 700 (kg) [Solution] With the corresponding solution Because now the total weight of flour and rice can be seen as the original 4800 kg and shipped The sum of a batch of flour, so now the weight of the flour is equivalent to 1/6 and 4,800 kg