答得好重赏.水丰乡三天修完一条水渠,第一天修了全长的2/5少12米,第二天修剩下1/3还多28米,第三天修了180米,这条水渠全长多少米?(请解释清楚)
来源:学生作业帮助网 编辑:作业帮 时间:2024/07/06 20:17:19
![答得好重赏.水丰乡三天修完一条水渠,第一天修了全长的2/5少12米,第二天修剩下1/3还多28米,第三天修了180米,这条水渠全长多少米?(请解释清楚)](/uploads/image/z/8792638-70-8.jpg?t=%E7%AD%94%E5%BE%97%E5%A5%BD%E9%87%8D%E8%B5%8F.%E6%B0%B4%E4%B8%B0%E4%B9%A1%E4%B8%89%E5%A4%A9%E4%BF%AE%E5%AE%8C%E4%B8%80%E6%9D%A1%E6%B0%B4%E6%B8%A0%2C%E7%AC%AC%E4%B8%80%E5%A4%A9%E4%BF%AE%E4%BA%86%E5%85%A8%E9%95%BF%E7%9A%842%EF%BC%8F5%E5%B0%9112%E7%B1%B3%2C%E7%AC%AC%E4%BA%8C%E5%A4%A9%E4%BF%AE%E5%89%A9%E4%B8%8B1%EF%BC%8F3%E8%BF%98%E5%A4%9A28%E7%B1%B3%2C%E7%AC%AC%E4%B8%89%E5%A4%A9%E4%BF%AE%E4%BA%86180%E7%B1%B3%2C%E8%BF%99%E6%9D%A1%E6%B0%B4%E6%B8%A0%E5%85%A8%E9%95%BF%E5%A4%9A%E5%B0%91%E7%B1%B3%3F%EF%BC%88%E8%AF%B7%E8%A7%A3%E9%87%8A%E6%B8%85%E6%A5%9A%EF%BC%89)
答得好重赏.水丰乡三天修完一条水渠,第一天修了全长的2/5少12米,第二天修剩下1/3还多28米,第三天修了180米,这条水渠全长多少米?(请解释清楚)
答得好重赏.
水丰乡三天修完一条水渠,第一天修了全长的2/5少12米,第二天修剩下1/3还多28米,第三天修了180米,这条水渠全长多少米?(请解释清楚)
答得好重赏.水丰乡三天修完一条水渠,第一天修了全长的2/5少12米,第二天修剩下1/3还多28米,第三天修了180米,这条水渠全长多少米?(请解释清楚)
解题思路:逆向思维
第三天修前180m
第二天修前(180+28)/(1-1/3)=312m
第二天修前(312-12)/(1-2/5)=500m
500米
假设全长为N 第一天修了 2/5xN-12, 第二天修了1/3xN+28 ,第三天修了180. 三天修完也就是总长N ,列式就是 (2/5xN-12)+(1/3xN+28)+180=N