請幫忙啊 prep-ds-41

peiswanho

41.    3690-!-item-!-187;#058&003497

Machines X and Y work at their respective constant rates.  How many more hours does it take machine Y, working alone, to fill a production order of a certain size than it takes machine X, working alone?



(1) Machines X and Y, working together, fill a production order of this size in two-thirds the time that machine X, working alone, does.



(2) Machine Y, working alone, fills a production order of this size in twice the time that machine X, working alone, does.



答案是E

詳解版對第二個解答是寫

1/y=2*1/x

但總覺得應該是

1/x=2*1/y才對呀

因為y要花上比x多兩倍時間

所以y會做比較慢不是嗎?

有誰能解答一下這題?

感謝~~~

Janeslove

首先，这两个条件都只能求出X和Y的比例关系，但是得不到具体的数字，题目问的是要多花多少小时，所以2个条件均无法求解

我不知道LZ那个解释是哪里的，我猜可能LZ把X，Y所代表的意思搞混了，原题的解释中XY代表的是他们分别的生产速度吧，而LZ的公式设的是时间

ywsunny

我觉得要是设X的时间为x hour,Y的时间为y hour的话··
应该是1)    2/3(1/x+y/1)=1/x
         2)    y=2x