弱问Prep DS1 41

girlwithwings · 发表于 2010-6-20 04:24:46

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】E

設work=1, machineX=Xhour, machineY=Yhour, 問y-x=?

我的理解是从（2）来看，Y比X没效率，同是完成1项任务，Y的耗时是X的2倍，也就是y =2x , 或者用速度来表示就是 2/y = 1/x

这个刚好和详解版的列式相反。

请NN讲解我的理解哪里错了？

yizhutou1 · 发表于 2010-6-20 05:21:34

通过条件2 就如你说的很快可得出x,y的速度比是 2:1
通过条件1 其实也可以算出 x和y的速度比为2比1

但是这两个条件里算出来的都只是比值完全没有涉及具体的 hours.

所以E

ywsunny · 发表于 2011-4-28 09:33:31

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

appletree1987 · 发表于 2013-8-16 06:51:53

以下摘录自曼哈顿论坛, 原帖请看 http://www.manhattangmat.com/forums/machine-x-and-y-work-at-their-respective-constant-rates-ds-t4339.html

Let x and y represent the respective rates of X and Y.
We must know the values of both x and y to know “how many more hours”. In other words, y = 2x does not tell us how many more hours the job takes Y than X, only that Y takes twice as long. If x = 2, y = 4 and the difference is 2. However, if x = 3, y = 6, and it now takes 3 hours longer.

1) 1/x + 1/y = 1/T
So, T (total time) = xy / (x+y)
Statement 1 tells us that the total time or combined = 2/3 x
So, xy / (x+y) = 2/3 x
Solve and you get y = 2x
INSUFFICIENT – again, it only gives us a relationship

2) translated gives y = 2x

Statements 1 and 2 provide the same information, so either D or E
Since we cannot combine 2 similar equations to solve for 2 variables, the answer is E

Juliana晶 · 发表于 2014-3-15 17:36:05

appletree1987 发表于 2013-8-16 06:51
以下摘录自曼哈顿论坛, 原帖请看 http://www.manhattangmat.com/forums/machine-x-and-y-work-at-their-res ...

D谢！！

弱问Prep DS1 41

所属分类: GMAT考试

正在浏览此版块的会员 ()

浏览过的版块