作者stephanini (Lit.S)
看板GMAT
标题Re: [计量] PP1-DS-41
时间Fri Nov 20 00:05:06 2009
应该是这样吧
1) 1/(1/X+1/Y)=(2/3)X
化简後变成=> XY/(X+Y)=(2/3)X
求不出来
2)Y=2X 也求不出来
两个合并後也不行
所以答案E
※ 引述《clearfuture (really?)》之铭言：
: 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.
: (解)
: 设work=1, machineX=Xhour, machineY=Yhour, 问y-x=?
: (1) 1/X + 1/Y = 2/3 ^ 1/X
: (2) 1/Y = 2^ 1/X
: 答案是E
: 可是直觉上两个变数，配上两条式子，为什麽不是C ?: 请高手指点迷津，谢谢!!
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1F：推 clearfuture:谢谢...本来想说看到两个变数,两条式子,就给他C了... 11/20 10:52