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Six machines, each working at the same constant rate,

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Manager
Joined: 30 Jan 2006
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Six machines, each working at the same constant rate, [#permalink]  06 Apr 2006, 14:24
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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?

This one is easy to solve, but I'm interested in finding out in how many different ways people can solve this. Please explain your answers.
Manager
Joined: 09 Feb 2006
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Location: New York, NY
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Well there is the easy way.

w=rt
1 = r12
1/12 = r

Each machine has a rate of 1/72.

To determine how many machines we need, let x be the number of machines.

1 = (x/72)*8
1 = x/9

x = 9

You need 9 machines to complete the job is 8 days.
Manager
Joined: 30 Jan 2006
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Thanks guys
Intern
Joined: 02 Feb 2006
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Doesn't the question ask for the number of ADDITONAL machines necessary to complete the job in 8 days?
Manager
Joined: 21 Dec 2005
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anbu wrote:
Doesn't the question ask for the number of ADDITONAL machines necessary to complete the job in 8 days?

You are right,,I agree with you. So answer is 3 machines.
Intern
Joined: 18 Apr 2006
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GMAT trap
VP
Joined: 08 Jun 2005
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I have a different approach.
If 6 machines do the work in 12 days,
to do the same work in 8 days you have to work 1.5 times as hard
meaning 6 x 1.5 = 9 machines

So the answer is 9 - 6 = 3
Manager
Joined: 27 Jan 2006
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easy tips

6*12=X*8

X=9

so 3 more machine needed
Intern
Joined: 14 Jan 2006
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Location: Visakhapatnam, India
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Machines : Days : Work
6 : 12 : 1 (6 machines complete in 12 days 1 work)
? : 8 : 1 (How many machines complete in 8 days 1 work)

? = 12*6/8 = 9
Therefore, 3 more machines required.[/list]
Manager
Joined: 27 Mar 2006
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Agree with 3
Senior Manager
Joined: 29 Jun 2005
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Agree with 3.
One machine can complete a job in 72 days - 72*1/6=12. 72*1/x=8  x=9. So, 9-6=3. Three additional machines are needed.
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