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# Working alone at its own constant rate, a machine seals k

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Working alone at its own constant rate, a machine seals k [#permalink]

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17 Nov 2010, 08:35
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Working alone at its own constant rate, a machine seals k cartoons in 8 hours, and working at its own constant rate a second machine seals k cartoons in 4 hours. if 2 machines each working at its own constant rate and for the same period of time together sealed a certain no of cartoons. what percentage of the cartoons were sealed by the machine working at the faster rate?

A. 25%
B. 33 1/3%
C. 50%
D. 66 2/3%
E. 75%
[Reveal] Spoiler: OA
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Re: working alone at its own constant rate [#permalink]

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17 Nov 2010, 08:38
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anilnandyala wrote:
working alone at its own constant rate, a machine seals k cartoons in 8 hours, and working at its own constant rate a second machine seals k cartoons in 4 hours. if 2 machines each working at its own constant rate and for the same period of time together sealed a certain no of cartoons. what percentage of the cartoons were sealed by the machine working at the faster rate?
a 25%
b 33 1/3%
c 50%
d 66 2/3%
e 75%

i am missing something in this, please explain thanks in advance

As second one works twice as fast as the first, working together second will do 2/3 of work and the first 1/3 of work (their ratio 1/2).

Answer: D.
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Re: working alone at its own constant rate [#permalink]

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17 Nov 2010, 09:03
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anilnandyala wrote:
working alone at its own constant rate, a machine seals k cartoons in 8 hours, and working at its own constant rate a second machine seals k cartoons in 4 hours. if 2 machines each working at its own constant rate and for the same period of time together sealed a certain no of cartoons. what percentage of the cartoons were sealed by the machine working at the faster rate?
a 25%
b 33 1/3%
c 50%
d 66 2/3%
e 75%

i am missing something in this, please explain thanks in advance

or think of it this way:
First machine seals k cartons in 8 hours.
Second machine seals k cartons in 4 hours i.e. 2k cartons in 8 hours.

If they both are working for the same period of time i.e. 8 hours, they together seal 3k cartons. Faster machine (second one) seals 2k out of these 3k so it seals 2/3 = 66.66% of the total cartons.
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Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Manager Status: Completed GMAT on 22 Nov 2011 Joined: 08 Nov 2010 Posts: 167 Followers: 10 Kudos [?]: 64 [1] , given: 12 Re: working alone at its own constant rate [#permalink] ### Show Tags 23 May 2011, 20:52 1 This post received KUDOS I solved it this way: Step 1: In one hour, the amount of work completed by Machine 1 is 1/8 and the amount of work completed by Machine 2 is ¼ i.e. Machine 2 works twice as fast as Machine 1. (You can get the answer in Step 1 only. Anyhow, you will understand how to get the answer in the Step 1 by using a shortcut in Step 3) Step 2: In two hours, the amount of work completed by Machine 1 is 2/8 and the amount of work completed by Machine 2 is 2/4. ⇨ Total work completed in 2 hours by 2 machines = (2/8)+(2/4) => (1/4) + (1/2) => 0.25+0.50 = 0.75. ⇨ So the total amount of work completed by both the machines is 75 %. Out of the 75%, Machine 1 completes 50% of the work and Machine 2 completes 25% of the work. Step 3: Only 25% of the work is left. So the remaining work has to be divided between Machine 1 and Machine 2. As we know, Machine 2 can do the work twice as fast as Machine 1. For example, if Machine 1 can do 10% of the work, Machine 2 can do 20% of the work in the same time. So, together they will complete 30% of the work. So from this example, we can understand that any work can be divided into 3 parts, and if Machine 1 completes 1 part of the work, and Machine 2 completes 2 parts of the work in the same time, irrespective of the quantum of work. Now, the pending work is 25%. Let’s divide the work into 3 equal parts i.e. 8.33% per part. So, Machine 1 will complete 8.33% of the work whereas Machine 2 will complete 16.66% of the work, which is remaining. So the total work completed by Machine 1 = 25%+8.33% = 33.33% The total work completed by Machine 2 = 50% + 16.66% = 66.66% So, the answer is (D) We can apply Step 3 in Step 1 to get the solution faster, avoiding all the unnecessary calculations of Step 2 and Step 3. VP Status: There is always something new !! Affiliations: PMI,QAI Global,eXampleCG Joined: 08 May 2009 Posts: 1353 Followers: 17 Kudos [?]: 217 [1] , given: 10 Re: working alone at its own constant rate [#permalink] ### Show Tags 23 May 2011, 21:34 1 This post received KUDOS if each one has worked for 8 hrs then number of cartoons = k + 2k = 3k. Mac B produces 2k of these. hence % = 2k/3k = 66.66% _________________ Visit -- http://www.sustainable-sphere.com/ Promote Green Business,Sustainable Living and Green Earth !! Manager Joined: 25 May 2011 Posts: 157 Followers: 2 Kudos [?]: 56 [0], given: 71 Re: working alone at its own constant rate [#permalink] ### Show Tags 30 Oct 2011, 10:13 Prefer Bunuel's approach Director Status: No dream is too large, no dreamer is too small Joined: 14 Jul 2010 Posts: 649 Followers: 39 Kudos [?]: 724 [2] , given: 39 Re: working alone at its own constant rate [#permalink] ### Show Tags 18 Dec 2011, 10:59 2 This post received KUDOS I solved the problem directly Rate one machine = k/8 Rate of the other machine = k/4 Total k/8+ k/4 = 3k/8 Faster seal to total seal = k/4 x 8/k = 66.33 Ans. D _________________ Collections:- PSof OG solved by GC members: http://gmatclub.com/forum/collection-ps-with-solution-from-gmatclub-110005.html DS of OG solved by GC members: http://gmatclub.com/forum/collection-ds-with-solution-from-gmatclub-110004.html 100 GMAT PREP Quantitative collection http://gmatclub.com/forum/gmat-prep-problem-collections-114358.html Collections of work/rate problems with solutions http://gmatclub.com/forum/collections-of-work-rate-problem-with-solutions-118919.html Mixture problems in a file with best solutions: http://gmatclub.com/forum/mixture-problems-with-best-and-easy-solutions-all-together-124644.html Senior Manager Joined: 12 Oct 2011 Posts: 272 Followers: 0 Kudos [?]: 41 [0], given: 110 Re: working alone at its own constant rate [#permalink] ### Show Tags 06 Jan 2012, 00:17 As the second machine works twice as fast as does the first one, the second machine will do twice as much work as does the first one. Together, if they complete a job, the second machine has worked twice as much as has the first machine. Thus, work done by second machine relative to the total work done is 2/3 => 66.67% Answer: D _________________ Consider KUDOS if you feel the effort's worth it GMAT Club Legend Joined: 09 Sep 2013 Posts: 11038 Followers: 509 Kudos [?]: 133 [0], given: 0 Re: Working alone at its own constant rate, a machine seals k [#permalink] ### Show Tags 18 Sep 2013, 18:07 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). Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________ GMAT Club Legend Joined: 09 Sep 2013 Posts: 11038 Followers: 509 Kudos [?]: 133 [0], given: 0 Re: Working alone at its own constant rate, a machine seals k [#permalink] ### Show Tags 28 Dec 2014, 11:04 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). Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________ EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 7146 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: 340 Q170 V170 Followers: 310 Kudos [?]: 2119 [0], given: 161 Re: Working alone at its own constant rate, a machine seals k [#permalink] ### Show Tags 28 Dec 2014, 15:10 Hi All, Even if you don't see the immediate ratios involved, you can still answer this question rather easily by TESTing VALUES. Here's how: We're told about 2 machines: Machine A can produce K cartons in 8 hours Machine B can produce K cartons in 4 hours Let's TEST K = 2 So.... Machine A = 2 cartons every 8 hours Machine B = 2 cartons every 4 hours We're told that each machine works on its own for the SAME amount of time. Let's say they both work for 8 hours. This means... Machine A seals 2 cartons Machine B seals 4 cartons Total = 6 cartons The question asks what ratio of the cartons the faster machine sealed. Machine B is the faster machine, and it sealed 4/6 of the cartons. 4/6 = 2/3 = 66 2/3% Final Answer: [Reveal] Spoiler: D GMAT assassins aren't born, they're made, Rich _________________ # Rich Cohen Co-Founder & GMAT Assassin # Special Offer: Save$75 + GMAT Club Tests

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Re: Working alone at its own constant rate, a machine seals k [#permalink]

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Rate of Machine A $$= \frac{k}{8}$$

Rate of Machine B $$= \frac{k}{4}$$

Combined rate of A & B $$= \frac{k}{8} + \frac{k}{4} = \frac{3k}{8}$$

Say they work for 1 hour

Work done by faster machine (Machine B) $$= \frac{k}{4} * 1 = \frac{k}{4}$$

Combined work done in 1 hour $$= \frac{3k}{8} * 1 = \frac{3k}{8}$$

Percentage work of faster machine $$= \frac{\frac{k}{4}}{\frac{3k}{8}} * 100 = \frac{200}{3} = 66.66%$$

Answer = D
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Re: Working alone at its own constant rate, a machine seals k [#permalink]

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10 Jan 2015, 12:51
I used the same aproach as Paresh. So, after finding the comdined rate as 3k/8, I assumed that they work for 1 hour. So, the individual work should be the same as the individual rates, i.e. k/8 for the slower one and k/4 for the faster one. It is then (k/4)/(3k/8).

What I didn't understand in the other approaches is why we used 8 hours as the amount of hours they worked for. I guess, we could also have chosen 4 hours or any other amount of hours?
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Re: Working alone at its own constant rate, a machine seals k [#permalink]

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10 Jan 2015, 13:02
Hi pacifist85,

You are correct - we could use ANY number of hours when TESTing VALUES. However, since the prompt offers us two rates that are based on 8 hours of work and 4 hours of work, respectively, choosing 8 hours allows us to make the calculations as simple as possible. In many Quant questions on Test Day, the specific numbers that appear in the prompt (and in the Answer choices) can help you to make choices that will get you to the correct answer in the fastest/easiest way possible.

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# Special Offer: Save $75 + GMAT Club Tests 60-point improvement guarantee www.empowergmat.com/ ***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*********************** Senior Manager Status: Math is psycho-logical Joined: 07 Apr 2014 Posts: 443 Location: Netherlands GMAT Date: 02-11-2015 WE: Psychology and Counseling (Other) Followers: 2 Kudos [?]: 92 [0], given: 169 Re: Working alone at its own constant rate, a machine seals k [#permalink] ### Show Tags 10 Jan 2015, 13:31 Thank you Rich. I was just wondering the reason why, since - as they were supposed to be working for some time - my intuition would be to use 1 hour, so I wouldn't have to calculate anything. As I am not used to doing quick calculations and haven't achieved to immediately see the connection between numbers yet (except for finding the LCM which I have managed to do almost instantly!!!!!) I was wondering if there was a reasoning I should know about and can use during the actual test. Thank god, I only need a 650, which is not really a low score for a psychologist to achieve... I am around the 600ts at the moment and can do most of the problems. However, calculations and time are the problem with me... So, this is helpful! Thanx! SVP Status: The Best Or Nothing Joined: 27 Dec 2012 Posts: 1858 Location: India Concentration: General Management, Technology WE: Information Technology (Computer Software) Followers: 37 Kudos [?]: 1658 [0], given: 193 Re: Working alone at its own constant rate, a machine seals k [#permalink] ### Show Tags 11 Jan 2015, 07:25 pacifist85 wrote: I used the same aproach as Paresh. So, after finding the comdined rate as 3k/8, I assumed that they work for 1 hour. So, the individual work should be the same as the individual rates, i.e. k/8 for the slower one and k/4 for the faster one. It is then (k/4)/(3k/8). What I didn't understand in the other approaches is why we used 8 hours as the amount of hours they worked for. I guess, we could also have chosen 4 hours or any other amount of hours? LCM of 4 & 8 is 8..... Its just for ease of calculation...... _________________ Kindly press "+1 Kudos" to appreciate EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 7146 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: 340 Q170 V170 Followers: 310 Kudos [?]: 2119 [0], given: 161 Re: Working alone at its own constant rate, a machine seals k [#permalink] ### Show Tags 11 Jan 2015, 16:09 Hi pacifist85, Here's an interesting "drill" that you can do to help develop this skill. Go back and review all of the past Quant questions that you've done and look for situations in which TESTing VALUES is applicable. When you come across those questions, look for the various "clues" in the prompt that would help you make a smart choice for the value(s) that you'd pick. Look for what's listed in the answers, the wording/descriptions in the prompt, any fractions that you're given, etc. For example, when I see the % sign in the answers, my first thought is that I might be able to TEST the number 100 in this question... In this way, you'll be training to not only spot the potential uses for this tactic, but you'll also be training to test the values that will make solving the problem most efficient. GMAT assassins aren't born, they're made, Rich _________________ # Rich Cohen Co-Founder & GMAT Assassin # Special Offer: Save$75 + GMAT Club Tests

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Working alone at its own constant rate, a machine seals k [#permalink]

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25 Nov 2015, 13:30
anilnandyala wrote:
Working alone at its own constant rate, a machine seals k cartoons in 8 hours, and working at its own constant rate a second machine seals k cartoons in 4 hours. if 2 machines each working at its own constant rate and for the same period of time together sealed a certain no of cartoons. what percentage of the cartoons were sealed by the machine working at the faster rate?

A. 25%
B. 33 1/3%
C. 50%
D. 66 2/3%
E. 75%

Rate A = $$\frac{1}{8}$$, Rate B =$$\frac{1}{4}$$ --> $$\frac{Rate A}{Rate B}=\frac{1}{8}*\frac{4}{1} = \frac{1}{2}$$ So the faster rate has 2 of 3 --> 66 2/3% Answer D
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Working alone at its own constant rate, a machine seals k   [#permalink] 25 Nov 2015, 13:30
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# Working alone at its own constant rate, a machine seals k

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