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Re: Work Rate Questions - I collected from GMAT Club [#permalink]

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22 Jul 2014, 03:55

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: Work Rate Questions - I collected from GMAT Club [#permalink]

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28 Dec 2014, 05:23

For Q8 there is an easy approach to think about it. This is actually thw working together scenario, with one twist. So, when machines work together, you add their individual rates to find the average rate. When one is undoing the work of the other what you do is subtract the rates. In the RT=W chart, we fill in the info we know:

R T W Filling valve 1/4 10 1 Draining valve 1/5 x 1

Now, the chart is creating an equation, but we need to pay attention to subtract the rates instead of adding them: (1/4)*10 - (1/5)x = 1 (50-4x)/20=1 50-4x=20 4x=30 x=7.5

Looking at the chart, x is the time the draining valve was working. So, from the time it took to fill the whole pool we subtract the time the draining valve was working: 23-7.5= 15.5 or 3.30 | 11-7.5=3.5 if you prefer, which in terms of time is 3 hours plus half an hour which is 3.30.

Re: Work Rate Questions - I collected from GMAT Club [#permalink]

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06 Feb 2015, 02:39

solution for number 2 : E (12 )

R * T = W for machine y : 1 /t * t =1 for machine x : 1 / (t+2) * (t+2) =1 both together : 5 /12 * 12/5 = 1 ( calculated the rate 5/12 from the given information)

the single rates are together the combined rate. ( 1/t + 1/(t+2)) = 5/12 solving for t (using pq formula).

t = 4 (second solution is negative, not relevant )

how many days does machine x need to produce 2 w? We know know the rate of machine x ( 1/(t+2) = 1 /(2+4)

Re: Work Rate Questions - I collected from GMAT Club [#permalink]

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12 Feb 2016, 06:48

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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