一道DS有疑问，大家来看看~~~

tangbobin

DS:Machines X and Y work at their respective constant rates. How many 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 produciton order of this size in two-thirds the time the 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.
这事PREP上的一道数学，我觉得选D，可是答案是E。。。求解释

你说过等我

设时间为X、Y。1和2算出来的结果都是2X=Y。没有具体value，所以应该是E吧。。。