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ps- machines

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Intern
Joined: 27 Aug 2005
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ps- machines [#permalink]  13 Sep 2005, 17:34
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6 Machines, each working at a constant rate, together can complete the job in 12 days. How many additional machines, working at the same rate are needed to complete the job in 8 days.
1. 2
2. 3
3. 4
4. 5
5. 1
Manager
Joined: 15 Jul 2005
Posts: 105
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1) 3 more machines are needed.

6 machines - 12 days
1 machine - 72 days
9 machines - 8 days
Senior Manager
Joined: 30 Oct 2004
Posts: 286
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Same here. I get 3.
We know they work at a constant rate... say each machine take T days
6 machines .. it takes 12 days
so, 6/T = 1/12
Lets say N machines take 8 days
so, N/T = 1/8
Substitue value of T in either equation
you get N = 9
So 3 more machines.
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-Vikram

Manager
Joined: 26 Jun 2005
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This is a direct variation problem. 12*6=8X, X=9. Three additional machines are needed.
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Chet

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