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?
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12
让w=1,设生产速度为x,y
用生产时间列式
1/x-1/y=2
(5/4)/(x+y)=3 化简得x+y=5/12
选项/2=1/x,代入列的式子里,找出符合的数字
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