Jul 14 08:00 PM PDT  09:00 PM PDT A better GRE prep experience. We believe GRE prep should be real education that prepares you not just for the test, but for the challenges you’ll face as you earn your graduate degree and advance your career. Jul 15 08:00 PM PDT  09:00 PM PDT Regardless of whether you choose to study with Greenlight Test Prep, I believe you'll benefit from my many free resources. Jul 22 07:30 AM PDT  08:30 AM PDT Learn the basics of quadratics to demystify one of the most commonly feared concepts on the GRE and GMAT.
Author 
Message 
TAGS:


Retired Moderator
Joined: 07 Jun 2014
Posts: 4804
WE: Business Development (Energy and Utilities)
Followers: 163
Kudos [?]:
2775
[2]
, given: 394

QOTD#9 In a factory, machine A operates on a cycle of 20 [#permalink]
12 Sep 2016, 11:31
2
This post received KUDOS
Question Stats:
41% (02:08) correct
58% (02:29) wrong based on 121 sessions
In a factory, machine A operates on a cycle of 20 hours of work followed by 4 hours of rest,and machine B operates on a cycle of 40 hours of work followed by 8 hours of rest. Last week, the two machines began their respective cycles at 12 noon on Monday and continued until 12 noon on the following Saturday. On which days during that time period was there a time when both machines were at rest? Indicate all such days.A. Monday B. Tuesday C. Wednesday D. Thursday E. Friday F. Saturday Practice Questions Question: 19 Page: 207
_________________
Sandy If you found this post useful, please let me know by pressing the Kudos Button
Try our free Online GRE Test




GRE Instructor
Joined: 10 Apr 2015
Posts: 3535
Followers: 133
Kudos [?]:
4012
[1]
, given: 65

Re: QOTD#9 In a factory, machine A operates on a cycle of 20 [#permalink]
20 Sep 2016, 14:44
1
This post received KUDOS
ExplanationLet's focus on 1 machine at a time and list the starting and stopping time. We'll start with Machine AMONDAY12 noon: Machine A startsTUESDAY8:00 am: Machine A stops12:00 noon: Machine A startsWEDNESDAY8:00 am: Machine A stops12:00 noon: Machine A startsTHURSDAY8:00 am: Machine A stops12:00 noon: Machine A startsFRIDAY8:00 am: Machine A stops12:00 noon: Machine A startsSATURDAY8:00 am: Machine A stops12:00 noon: Machine A starts Now let's add Machine BMONDAY12 noon: Machine A starts12 noon: Machine B starts TUESDAY8:00 am: Machine A stops12:00 noon: Machine A startsWEDNESDAY4:00 am: Machine B stops8:00 am: Machine A stops12:00 noon: Machine A starts12:00 noon: Machine B startsTHURSDAY8:00 am: Machine A stops12:00 noon: Machine A startsFRIDAY4:00 am: Machine B stops8:00 am: Machine A stops12:00 noon: Machine A starts12:00 noon: Machine B startsSATURDAY8:00 am: Machine A stops12:00 noon: Machine A startsAs we can see, both machines are stopped at the same time on Wednesday and Friday. Answer: C and E Cheers, Brent
_________________
Brent Hanneson – Creator of greenlighttestprep.com Sign up for my free GRE Question of the Day emails



Manager
Joined: 21 Oct 2015
Posts: 64
Followers: 0
Kudos [?]:
19
[0], given: 4

Re: QOTD#9 In a factory, machine A operates on a cycle of 20 [#permalink]
29 May 2017, 19:57
is there any quicker method to do this calculation? GreenlightTestPrep wrote: sandy wrote: In a factory, machine A operates on a cycle of 20 hours of work followed by 4 hours of rest,and machine B operates on a cycle of 40 hours of work followed by 8 hours of rest. Last week, the two machines began their respective cycles at 12 noon on Monday and continued until 12 noon on the following Saturday. On which days during that time period was there a time when both machines were at rest?
Indicate all such days.
A. Monday B. Tuesday C. Wednesday D. Thursday E. Friday F. Saturday
Let's focus on 1 machine at a time and list the starting and stopping time. We'll start with Machine AMONDAY12 noon: Machine A startsTUESDAY8:00 am: Machine A stops12:00 noon: Machine A startsWEDNESDAY8:00 am: Machine A stops12:00 noon: Machine A startsTHURSDAY8:00 am: Machine A stops12:00 noon: Machine A startsFRIDAY8:00 am: Machine A stops12:00 noon: Machine A startsSATURDAY8:00 am: Machine A stops12:00 noon: Machine A starts Now let's add Machine BMONDAY12 noon: Machine A starts12 noon: Machine B starts TUESDAY8:00 am: Machine A stops12:00 noon: Machine A startsWEDNESDAY4:00 am: Machine B stops8:00 am: Machine A stops12:00 noon: Machine A starts12:00 noon: Machine B startsTHURSDAY8:00 am: Machine A stops12:00 noon: Machine A startsFRIDAY4:00 am: Machine B stops8:00 am: Machine A stops12:00 noon: Machine A starts12:00 noon: Machine B startsSATURDAY8:00 am: Machine A stops12:00 noon: Machine A startsAs we can see, both machines are stopped at the same time on Wednesday and Friday.



Manager
Joined: 08 Dec 2018
Posts: 94
Followers: 0
Kudos [?]:
41
[0], given: 30

Re: QOTD#9 In a factory, machine A operates on a cycle of 20 [#permalink]
15 Jun 2019, 09:01
both machines should stop at a 40 hours interval [ as the LCM of 20,40 is 40] so, starting from 12.00 noon of Monday we can take a 40 hour working time followed by a rest . thus, 12noo+40 hours lead to a rest on Wednesday again another 40 hours, now it's on Friday.



Intern
Joined: 27 Apr 2019
Posts: 3
Followers: 0
Kudos [?]:
0
[0], given: 0

Re: QOTD#9 In a factory, machine A operates on a cycle of 20 [#permalink]
08 Oct 2019, 06:23
Yes we can find the LCM of total hours in order to have answer eg: LCM of 24 hrs and 48 hrs



Intern
Joined: 30 Oct 2019
Posts: 28
Followers: 0
Kudos [?]:
8
[1]
, given: 0

Re: QOTD#9 In a factory, machine A operates on a cycle of 20 [#permalink]
30 Oct 2019, 20:46
1
This post received KUDOS
Yes we can find the LCM of total hours in order to have answer eg: LCM of 24 hrs and 48 hrs



Intern
Joined: 25 Dec 2019
Posts: 11
Followers: 0
Kudos [?]:
5
[0], given: 19

Re: QOTD#9 In a factory, machine A operates on a cycle of 20 [#permalink]
29 Jan 2020, 23:14
i saw this question in the ETS practice book but was a bit confused by the wording... thought that "following saturday" meant we needed to calculate two weeks worth, which would mean it would include Monday... was wondering if that confused anyone else?



GRE Instructor
Status: Entrepreneur  GMAT, GRE, CAT, SAT, ACT coach & mentor  Founder @CUBIX  Educonsulting  Content creator
Joined: 19 Jan 2020
Posts: 112
GMAT 1: 740 Q51 V39
GPA: 3.72
Followers: 5
Kudos [?]:
125
[1]
, given: 1

Re: QOTD#9 In a factory, machine A operates on a cycle of 20 [#permalink]
30 Jan 2020, 04:15
1
This post received KUDOS
sandy wrote: In a factory, machine A operates on a cycle of 20 hours of work followed by 4 hours of rest,and machine B operates on a cycle of 40 hours of work followed by 8 hours of rest. Last week, the two machines began their respective cycles at 12 noon on Monday and continued until 12 noon on the following Saturday. On which days during that time period was there a time when both machines were at rest? Indicate all such days.A. Monday B. Tuesday C. Wednesday D. Thursday E. Friday F. Saturday Practice Questions Question: 19 Page: 207 For Machine A: For 20 hours of work, it takes 4 hours rest => In a span of 24 hours, the last 4 hours are for rest ... (i) For Machine B: For 40 hours of work, it takes 8 hours rest => In a span of 48 hours, the last 8 hours are for rest ... (ii) Thus, for the last 4 hours (out of the 8 hours) when Machine B is at rest, Machine A is also at rest. This scenario occurs at the end of the 2nd day from when both A and B have started to work together Thus, in every 2 days (48 hours), both machines are at rest in the last 4 hours The machines start on Monday 12 noon # First time both rest are the last 4 hrs of the 2nd day i.e. 8 am to 12 noon of Wednesday(after this, both start working together from 12 noon of Wednesday) # Thus, the second time both rest are the last 4 hrs of the 2nd day from Wednesday i.e. 8 am to 12 noon of FridayThere would be no more opportunities of resting together since they work only till Saturday. Answers: C and E
_________________
Sujoy Kumar Datta Director  CUBIX Educational Institute Pvt. Ltd. (https://www.cubixprep.com) Admissions Consulting: http://www.oneclickprep.com/admissionsconsulting/ IIT Kharagpur, TU Dresden Germany Linkedin: https://www.linkedin.com/in/sujoykumardatta/ GMAT  Q51 & CAT (MBA @ IIM) 99.98 Overall with 99.99 QA Ask me anything about GRE _________ Feel free to talk to me about GMAT & GRE  Ask me any question on QA (PS / DS)  Let's converse! Skype: sk_datta, Alt. Email: sujoy.datta@gmail.com



Manager
Joined: 01 Jan 2020
Posts: 112
Concentration: Marketing
Schools: Copenhagen Business School  Class of 2022
Followers: 0
Kudos [?]:
54
[1]
, given: 46

Re: QOTD#9 In a factory, machine A operates on a cycle of 20 [#permalink]
27 May 2020, 05:51
1
This post received KUDOS
sandy wrote: In a factory, machine A operates on a cycle of 20 hours of work followed by 4 hours of rest,and machine B operates on a cycle of 40 hours of work followed by 8 hours of rest. Last week, the two machines began their respective cycles at 12 noon on Monday and continued until 12 noon on the following Saturday. On which days during that time period was there a time when both machines were at rest? Indicate all such days.A. Monday B. Tuesday C. Wednesday D. Thursday E. Friday F. Saturday Practice Questions Question: 19 Page: 207 With such exercises I feel they look harder then they are. Starting off with looking at mac a mac a works 20hr and then rests 4 hr Meaning that we would see their cycle looking like the following 20 work 4 rest= 24 hr, 24+20work + 4rest= 48 hr Now B goes 40 work + 8 rest =48hr , 48+40work+8rest= 96hr Now a thing we can spot or search for is how long does it take the lower one to catch up with the bigger one logic. We look at A> A will start their second round of rest at 44hr, which coincides with the rest of B. Meaning that at the beginning of every second rest from A the two will rest simultaneously. This leading us to the conclusion that every 44 hours the two will rest together for 4 hr. This would mean the first rest that the two will have together will be on WED>12+24+8=44>leaving us with 16 hr left in wed the next rest will be on friday 16+24+4=44>leaving us with 20+12 hr from friday and saturday which is not enough to get a rest in together Thereby getting the answers c and e



Intern
Joined: 24 Jun 2020
Posts: 1
Followers: 0
Kudos [?]:
0
[0], given: 1

Re: QOTD#9 In a factory, machine A operates on a cycle of 20 [#permalink]
24 Jun 2020, 17:05
anita123 wrote: Yes we can find the LCM of total hours in order to have answer eg: LCM of 24 hrs and 48 hrs Hi, can you explain me how you get the result by LCM? Thx,Regards




Re: QOTD#9 In a factory, machine A operates on a cycle of 20
[#permalink]
24 Jun 2020, 17:05





