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一、等差数列型例1 从材料工地运送电线杆到500米以外的公路的同一旁埋设,每隔50米在路边埋一根.已知每次只能运3根,要完成运20根电线杆的任务,并返回材料工地,问运输车的最少行程是多少米? 解析每次只能运3根,要完成运20根电线杆的任务,需要运7次,那么必有一次运2根,所以共有7种运法:第一次运2根,其他每次运3根,或第二次运
First, the arithmetic progression type example 1 The utility model is transported from the material site to the same side of the road 500 meters away, buried every 50 meters on the side of the road. It is known that only 3 can be transported each time. The task of the root pole, and return to the material site, asked how many meters is the minimum journey of the transport vehicle? Analysis can only transport 3 roots each time, to complete the task of transporting 20 power poles, need to transport 7 times, then there must be a transport 2 roots, so there are 7 ways of doing things: 2 for the first time, 3 for each other, or 2nd time