og math # 130
- jaspreetsra
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Printer Rate Time Work Doneresilient wrote:hmm still not seeing the picture. What I am trying to grasp is why the flip of the combined rates. It doesnt make sense to me and goes against what is taught with mahattan gmat. confused
thank you
X 1/12 12 1
Y 1/15 15 1
Z 1/18 18 1
Y+Z 11/90 *90/11 1
*Y+Z = 1/15 +1/18 =11/90
Ratio:
12: 90/11
=132:90
=22:15
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- Max@Math Revolution
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Forget conventional ways of solving math questions. In PS, IVY approach is the easiest and quickest way to find the answer.
working alone, printers x,y, and z can do a certain printing job, consisitning of a large number of pages, 12, 15, and 18 hours, respectively. What is the ratio of the time it takes printer x to do the job, working at its rate, to time it takes printers y and z to do the job, working together at their individual rates?
a. 4/11
b.1/2
c. 15/22
d.22/15
e.11/4
==> in case of power questions, we use the inverse numbers once we see 'together and alone'. In other words, since y and z worked together and took t hours, (1/15)=(1/18)=1/t, (6+5)/90=1/t, t=90/11 therefore 12:(90/11)=2:(15/11). multiplying 11 to both sides gives us 22:15, therefore D is the answer.
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working alone, printers x,y, and z can do a certain printing job, consisitning of a large number of pages, 12, 15, and 18 hours, respectively. What is the ratio of the time it takes printer x to do the job, working at its rate, to time it takes printers y and z to do the job, working together at their individual rates?
a. 4/11
b.1/2
c. 15/22
d.22/15
e.11/4
==> in case of power questions, we use the inverse numbers once we see 'together and alone'. In other words, since y and z worked together and took t hours, (1/15)=(1/18)=1/t, (6+5)/90=1/t, t=90/11 therefore 12:(90/11)=2:(15/11). multiplying 11 to both sides gives us 22:15, therefore D is the answer.
www.mathrevolution.com
l The one-and-only World's First Variable Approach for DS and IVY Approach for PS that allow anyone to easily solve GMAT math questions.
l The easy-to-use solutions. Math skills are totally irrelevant. Forget conventional ways of solving math questions.
l The most effective time management for GMAT math to date allowing you to solve 37 questions with 10 minutes to spare
l Hitting a score of 45 is very easy and points and 49-51 is also doable.
l Unlimited Access to over 120 free video lessons at https://www.mathrevolution.com/gmat/lesson
Our advertising video at https://www.youtube.com/watch?v=R_Fki3_2vO8
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Two important things in time and work :
if X completes work is x hrs, X RATE of work = 1/x
Y completes work is y hrs,Y RATE of work= 1/y
and they work together
1/x + 1/y = 1/h will give the total 'TIME' taken to complete the work (usually days)
where as 'h' gives total 'RATE' of combined x and y
that's why the flip happens
if X completes work is x hrs, X RATE of work = 1/x
Y completes work is y hrs,Y RATE of work= 1/y
and they work together
1/x + 1/y = 1/h will give the total 'TIME' taken to complete the work (usually days)
where as 'h' gives total 'RATE' of combined x and y
that's why the flip happens
Hello all,
so far I have only understood the answer from "GMATinsight" which makes totally sense.
I have a different approach and want to know why I can't proceed as followed:
the medium time of Printer y and z to finish the certain Job is 16,5 hours.
I divided the 16,5 by two because I assume that with the average time the two Printers will print twice as many as one Printer. The result should be proportioned to the result of the time Printer x Needs for this certain printing Job.
Thanks for your help in advance and Kind regards,
Max
so far I have only understood the answer from "GMATinsight" which makes totally sense.
I have a different approach and want to know why I can't proceed as followed:
the medium time of Printer y and z to finish the certain Job is 16,5 hours.
I divided the 16,5 by two because I assume that with the average time the two Printers will print twice as many as one Printer. The result should be proportioned to the result of the time Printer x Needs for this certain printing Job.
Thanks for your help in advance and Kind regards,
Max
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This is where intuition fails.maxmayr93 wrote:Hello all,
so far I have only understood the answer from "GMATinsight" which makes totally sense.
I have a different approach and want to know why I can't proceed as followed:
the medium time of Printer y and z to finish the certain Job is 16,5 hours.
I divided the 16,5 by two because I assume that with the average time the two Printers will print twice as many as one Printer. The result should be proportioned to the result of the time Printer x Needs for this certain printing Job.
Thanks for your help in advance and Kind regards,
Max
The time it takes for both Y and Z working together is as follows:
1 = T(1/18 + 1/15) . Solving for T yields 90/11 hours, or 8 2/11 hours.
So each of them working 8 2/11 hours will finish the job. This differs from a simple average you mention above of 8 1/4 hours.
2/11 = 8/44 versus 1/4 = 11/44 > your method has them working 3/44 longer as necessary.
The 15 and 18 hours can be viewed as a form of rate, which is a ratio, and you have to be very careful averaging ratios and how you interpret them
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x can do work by 12 hours
y and z together can do the work by 15.18 / (15+18)
x : y+z = 12 : 15 . 18 / 33 = 2 : 15 / 11 = 22 : 15
y and z together can do the work by 15.18 / (15+18)
x : y+z = 12 : 15 . 18 / 33 = 2 : 15 / 11 = 22 : 15
Rates are measured in inverse time. So the total rate of x and y together = 1/15 + 1/18 = 1/3(1/5 + 1/6) = 1/3(11/30) = 11/90
The total time is the reciprocal of this, namely 90/11.
The ratio required is x:(x and y) = 12: 90/11 = 12 x 11 /90 = 22/15 (D)
The total time is the reciprocal of this, namely 90/11.
The ratio required is x:(x and y) = 12: 90/11 = 12 x 11 /90 = 22/15 (D)
- deepak4mba
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