Running at their respective constant rates, machine X takes 2 days longer to produce w widgets than machine Y. At these rates, if the two machines together produce 5/4 w widgets in 3 days, how many days would it take machine X alone to produce 2w widgets?
4
6
8
10
12
转:设x用了x天做w个 y用了x-2天 则x一天做w\x,y一天w\(x-2)
3天x,y一起做了
3(w\x+w\(x-2))=5\4w
解方程 约掉w
12\x+12\(x-2)=5
化为整式方程得到(5x-4)(x-6)=0
x1=0.8 x2=6
检验两个都符合原方程但是x1不符合实际
所以x为6
所以x做2w用12天 选e
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