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1.分合调换有些工程问题的应用题,把条件中的“合做”“独做”,作适当的调换,易于建立起条件与条件之间的关系,从而找到解题思路。例1 甲乙两人合修一件工程要12天完成。如果让甲先做8天,剩下的工作由乙独做14天做完。乙独做这项工程需要几天? 初看起来,所给的条件之间联系不上,思路不通。我指导学生把“甲先做8天,乙独做14天”改变成“甲乙合做8天,乙再独做(14-8)天”,使甲乙合做的工作效率和1/12得以使用,顿时发现了新的数量关系,展开了思路。列式1÷[1-1/12×8)÷(14-8)]=18(天) 例2 一项工程,如果由甲队单独做,正好在计划规定时间完成。如果由乙队单独做,要超出计划规定时间3天才能完成。如果先由甲乙两队合做2
1. The division of exchange Some engineering problems in the application of the problem, the conditions of “cooperation” and “exclusive”, make the appropriate exchange, easy to establish the relationship between conditions and conditions, so as to find a solution to the problem. Example 1 A and B together to repair a project to be completed within 12 days. If you let a first eight days, the rest of the work done by the B alone 14 days. It takes a few days for B alone to do this project? At first glance, the conditions given are not linked, and the idea is not clear. I instruct the students to change “A first do 8 days, B alone do 14 days” into “A and B together for 8 days, B and then do alone (14-8) days,” so that A and B work efficiency and 1/12 to Use, suddenly found a new relationship between quantity, started thinking. Column 1 ÷ [1-1 / 12 × 8) ÷ (14-8)] = 18 (day) Example 2 A project, if done by Team A alone, was completed exactly on schedule. If the team B alone, to go beyond the scheduled time of 3 days to complete. If the first team by the two teams A and B 2