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 ~$5 \over 4$~ w widgets in 3 days, how many days would it take Machine X alone to produce 2W widgets?
4
6
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12
这一题运算量还是有点大,一分半钟可能还够呛,中间还需要十字相乘5Y^2-14Y-24=0,因式分解为 (5Y+6)(Y-4)=0, Y=4, X=6,所以X功率为W/6,所以2W再除以W/6=12.
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