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Six machines, each working at the same constant rate

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Re: Six machines, each working at the same constant rate  [#permalink]

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New post 01 Dec 2018, 12:33
Another option to solve this question is using Backsolving.

W= R x T
W= 6 machines x 12 days = 72 days for 1 machine to complete the job.

Now, we need to find "extra" machines that match "72 days per machine".

If we select:

A) 2 we will have 8 machines x 8 days = 64 days for 1 machine to complete the job. Not a match! Out!!

B) 3 we will have 9 machines x 8 days = 72 days for 1 machine to complete the same job in the same rate!! That's a match!

Answer: B


Thanks!
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Six machines, each working at the same constant rate  [#permalink]

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New post 08 Sep 2019, 07:13
Hi VeritasKarishma

I wish I could send you a gratitude note for your awesome time efficient approach mentioned
here :)

Please confirm your two cents:
Logic: more the nos of machines -> less no of days

Start with no of machines in initial stage:
6

Now we need to decide to multiply by 12/8 or 8/12
Since we need more no of machines to do the work in less time from 12 to 8 days , we need an improper fraction
hence
6 * (12/8) = 9 no of machines.

Additional machines = 9 - 6 = 3

Thanks for detailed post here too
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Re: Six machines, each working at the same constant rate  [#permalink]

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New post 09 Sep 2019, 07:17
1
adkikani wrote:
Hi VeritasKarishma

I wish I could send you a gratitude note for your awesome time efficient approach mentioned
here :)

Please confirm your two cents:
Logic: more the nos of machines -> less no of days

Start with no of machines in initial stage:
6

Now we need to decide to multiply by 12/8 or 8/12
Since we need more no of machines to do the work in less time from 12 to 8 days , we need an improper fraction
hence
6 * (12/8) = 9 no of machines.

Additional machines = 9 - 6 = 3

Thanks for detailed post here too


Yes, that's correct!
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Re: Six machines, each working at the same constant rate  [#permalink]

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New post 30 Sep 2019, 16:47
zz0vlb 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


6 machines --> 6r (rate) * 12 (time) = 1 Work
1 machine --> 1r * 72 = 1, we can say 1m = 72r
We need the n, number of machines to do the 1 Work in t=8
nr*8 = 72r, divide by r
n*8 = 72
n = 9
9-6 = 3
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Re: Six machines, each working at the same constant rate  [#permalink]

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New post 14 Oct 2019, 05:30
LalaB wrote:
6 machines in 12 hours can make 6*12=72 units.
x machines in 8 hours can make x*8=72 units x=9

12-9=3 more machines are needed
hope it helps


9-6=3
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Re: Six machines, each working at the same constant rate   [#permalink] 14 Oct 2019, 05:30

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