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有的分数、百分数应用题,初看起来 数量和分率都在变来变去。如年龄 问题中几个人的年龄及年龄倍数关 系总在不断变化,稀释溶液问题中, 溶液的浓度及重量都在变化。这些问题好象难以寻求解题途径,但只要我们认真分析题中的条件和问题,就能发现一个“变中不变”的量,以不变量为突破口,迅速找到解题途径。请看下面几例: 例1:某车间有职工180人,其中女职工占2/5,后来又招进一批女职工,这时女职工人数占职工总人数的2/3,又招进女工多少人?
Some of the scores, the percentage of application questions, initially looks like the number and rate are changing. Such as age problems in several people's age and age-fold relationship is constantly changing, dilute solution problems, the concentration and weight of the solution is changing. If these problems seem difficult to find a solution to the problem, as long as we carefully analyze the conditions and problems in the question, we can find a “constant change” amount and take invariants as a breakthrough point to quickly find a solution to the problem. Please see the following examples: Example 1: A workshop staff of 180 people, of which female staff accounted for 2/5, and later recruited a number of female workers, then the number of female workers accounted for 2/3 of the total number of workers, and recruit How many women workers?