标题: 一道DS有疑问，大家来看看~~~ [打印本页] 作者: tangbobin 时间: 2011-8-13 18:24 标题: 一道DS有疑问，大家来看看~~~ 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。。。求解释作者: 你说过等我 时间: 2011-8-13 18:45
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。。。