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## og math # 130

tagged by: Brent@GMATPrepNow

This topic has 8 expert replies and 121 member replies
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Shilpa77 Newbie | Next Rank: 10 Posts
Joined
20 Aug 2014
Posted:
6 messages
Sat Aug 23, 2014 9:49 am
Answer D : 22/15

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### GMAT/MBA Expert

Max@Math Revolution Legendary Member
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Wed Sep 02, 2015 9:39 pm
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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gouthami naidu Newbie | Next Rank: 10 Posts
Joined
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Posted:
1 messages
Sun Feb 21, 2016 9:49 pm
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

### GMAT/MBA Expert

Max@Math Revolution Legendary Member
Joined
24 Jul 2015
Posted:
846 messages
Followed by:
22 members
19
GMAT Score:
Wed Sep 02, 2015 9:39 pm
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.

www.mathrevolution.com
l The one-and-only Worldâ€™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 http://www.mathrevolution.com/gmat/lesson

gouthami naidu Newbie | Next Rank: 10 Posts
Joined
19 Feb 2016
Posted:
1 messages
Sun Feb 21, 2016 9:49 pm
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

### Top Member

regor60 Master | Next Rank: 500 Posts
Joined
15 Oct 2009
Posted:
197 messages
27
Mon Sep 25, 2017 9:49 am
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
This is where intuition fails.

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

maxmayr93 Newbie | Next Rank: 10 Posts
Joined
25 Sep 2017
Posted:
3 messages
Mon Sep 25, 2017 6:43 am
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

lb2012 Newbie | Next Rank: 10 Posts
Joined
30 Aug 2015
Posted:
4 messages
Tue Sep 01, 2015 1:55 am
D is correct

chanstee Newbie | Next Rank: 10 Posts
Joined
06 Mar 2015
Posted:
7 messages
Sat Jul 11, 2015 5:12 am
Answer is e 22/15

akash singhal Master | Next Rank: 500 Posts
Joined
24 Apr 2015
Posted:
152 messages
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3 members
2
GMAT Score:
650
Tue Apr 28, 2015 6:08 am
Simple calculation already explained...

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