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Machine A can complete a certain job in x hours. Machine B

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Joined: 07 May 2007
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Machine A can complete a certain job in x hours. Machine B [#permalink]

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16 Jul 2007, 16:25
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Machine A can complete a certain job in x hours. Machine B can complete the same job in y hours.
If A and B work together at their respective rates to complete the job, which of the following
represents the fraction of the job that B will not have to complete because of A's help?

a) (x-y)/(x+y)
b) x/(y-x)
c) (x+y)/xy
d) y/(x-y)
e) y/(x+y)
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Joined: 06 Apr 2007
Posts: 22
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16 Jul 2007, 20:54
A: 1/x B: 1/y

1/x + 1/y = x+y/xy

(1/x) / [(x+y)/xy] = y/x+y

(E)
16 Jul 2007, 20:54
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Machine A can complete a certain job in x hours. Machine B

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