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# Six machines, each working at the same constant rate,

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Manager
Joined: 05 Jan 2006
Posts: 66
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Six machines, each working at the same constant rate, [#permalink]

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21 May 2006, 14:51
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days?

(A) 2
(B) 3
(C) 4
(D) 6
(E) 8

Director
Joined: 24 Oct 2005
Posts: 659
Location: London
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21 May 2006, 14:56
6 machines - 12 days.
Therefore 1 machine = 12*6 days.
8 days - (12*6)/8 = 9 machines.

No of addn machines = 9-6 = 3

Ans = B
Senior Manager
Joined: 15 Mar 2005
Posts: 419
Location: Phoenix
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Re: Another rate question [#permalink]

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21 May 2006, 17:51
x242222 wrote:
Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days?

(A) 2
(B) 3
(C) 4
(D) 6
(E) 8

Another way:
12 days -> 8 days => Machines = 6*12/8 = 9. Thus additional machines = 3.
_________________

Who says elephants can't dance?

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Joined: 07 Jul 2004
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Location: Singapore
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21 May 2006, 22:41
Rate of each machine: 1 job in a hours, so 1/a job in 1 hour

Working together, 6/a job in 1 hour. So 1 job will take a/6 hours

a/6 = 12*24
a = 1728 hours

Assume we need n such machines

n/a job in 1 hour --> 1 job in a/n hours

1827/n = 8 * 24 =

n = 9

# of additional machines = 3
[#permalink] 21 May 2006, 22:41
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# Six machines, each working at the same constant rate,

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