推 clearfuture:謝謝...本來想說看到兩個變數,兩條式子,就給他C了... 11/20 10:52
應該是這樣吧
1) 1/(1/X+1/Y)=(2/3)X
化簡後變成=> XY/(X+Y)=(2/3)X
求不出來
2)Y=2X 也求不出來
兩個合併後也不行
所以答案E
※ 引述《clearfuture (really?)》之銘言：
: 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)
: 設work=1, machineX=Xhour, machineY=Yhour, 問y-x=?
: (1) 1/X + 1/Y = 2/3 ^ 1/X
: (2) 1/Y = 2^ 1/X
: 答案是E
: 可是直覺上兩個變數，配上兩條式子，為什麼不是C ?: 請高手指點迷津，謝謝!!
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