Author 
Message 
TAGS:

Hide Tags

Current Student
Status: Persevere
Joined: 09 Jan 2016
Posts: 120
Location: Hong Kong
GPA: 3.52

Five machines at a certain factory operate at the same constant rate
[#permalink]
Show Tags
24 May 2016, 23:19
Question Stats:
73% (01:05) correct 27% (01:32) wrong based on 686 sessions
HideShow timer Statistics
Five machines at a certain factory operate at the same constant rate. If four of these machines, operating simultaneously, take 30 hours to fill a certain production order, how many fewer hours does it take all five machines, operating simultaneously, to fill the same production order? (A) 3 (B) 5 (C) 6 (D) 16 (E) 24
Official Answer and Stats are available only to registered users. Register/ Login.




SC Moderator
Joined: 13 Apr 2015
Posts: 1706
Location: India
Concentration: Strategy, General Management
GPA: 4
WE: Analyst (Retail)

Re: Five machines at a certain factory operate at the same constant rate
[#permalink]
Show Tags
25 May 2016, 01:19
Total work done by 4 machines = 30 * 4 = 120 units
When one more machine is added each machine works for > 120/5 = 24 hours
Difference = 30  24 = 6hrs
Answer: C




Math Expert
Joined: 02 Aug 2009
Posts: 6789

Re: Five machines at a certain factory operate at the same constant rate
[#permalink]
Show Tags
25 May 2016, 07:34
nalinnair wrote: Five machines at a certain factory operate at the same constant rate. If four of these machines, operating simultaneously, take 30 hours to fill a certain production order, how many fewer hours does it take all five machines, operating simultaneously, to fill the same production order?
(A) 3 (B) 5 (C) 6 (D) 16 (E) 24 4 machines do a work in 30 days.. 1 machine will do that work in 30*4 days... 5 machines will do it in \(30*\frac{4}{5}= 24..\) lesser time = \(3024 = 6\) C
_________________
1) Absolute modulus : http://gmatclub.com/forum/absolutemodulusabetterunderstanding210849.html#p1622372 2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html 3) effects of arithmetic operations : https://gmatclub.com/forum/effectsofarithmeticoperationsonfractions269413.html
GMAT online Tutor



Board of Directors
Status: QA & VA Forum Moderator
Joined: 11 Jun 2011
Posts: 4020
Location: India
GPA: 3.5
WE: Business Development (Commercial Banking)

Re: Five machines at a certain factory operate at the same constant rate
[#permalink]
Show Tags
25 May 2016, 07:43
nalinnair wrote: Five machines at a certain factory operate at the same constant rate. If four of these machines, operating simultaneously, take 30 hours to fill a certain production order, how many fewer hours does it take all five machines, operating simultaneously, to fill the same production order?
(A) 3 (B) 5 (C) 6 (D) 16 (E) 24 Total work = 4*30 machine hrs Time taken = 4* 30 /5 => 24 hours... Thus all five machines, operating simultaneously will take ( 30  24 ) 6 hours.. Answer will be (C) 6
_________________
Thanks and Regards
Abhishek....
PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS
How to use Search Function in GMAT Club  Rules for Posting in QA forum  Writing Mathematical Formulas Rules for Posting in VA forum  Request Expert's Reply ( VA Forum Only )



Current Student
Joined: 18 Oct 2014
Posts: 874
Location: United States
GPA: 3.98

Re: Five machines at a certain factory operate at the same constant rate
[#permalink]
Show Tags
25 May 2016, 08:40
nalinnair wrote: Five machines at a certain factory operate at the same constant rate. If four of these machines, operating simultaneously, take 30 hours to fill a certain production order, how many fewer hours does it take all five machines, operating simultaneously, to fill the same production order?
(A) 3 (B) 5 (C) 6 (D) 16 (E) 24 If 4 machines take 30 hrs, 5 machines will take 30*4/5= 24 hrs How many fewer hours will all five machines take= 3024= 6 hrs C is the answer
_________________
I welcome critical analysis of my post!! That will help me reach 700+



Manager
Joined: 08 Nov 2015
Posts: 79

Re: Five machines at a certain factory operate at the same constant rate
[#permalink]
Show Tags
08 Jan 2017, 00:50
nalinnair wrote: Five machines at a certain factory operate at the same constant rate. If four of these machines, operating simultaneously, take 30 hours to fill a certain production order, how many fewer hours does it take all five machines, operating simultaneously, to fill the same production order?
(A) 3 (B) 5 (C) 6 (D) 16 (E) 24 Let the rate of machine be x hours. So in hour it can complete 1/x of work. Four machine rate = 4*(1/x) = 4/x. Now, Rate* Time = Job i.e. 4/x*30 = Job. So one machine can take 120 hour to complete the job. Five machine works together it can take :120/5 = 24 hours to complete the job. Hence 3024 = 6 hours. Answer is C.



Study Buddy Forum Moderator
Joined: 04 Sep 2016
Posts: 1196
Location: India
WE: Engineering (Other)

Five machines at a certain factory operate at the same constant rate
[#permalink]
Show Tags
20 May 2018, 20:29
Hi VeritasPrepKarishma chetan2u niks18 gmatbusters BunuelLet me know if my below approach is correct using 'Joint variation' as discussed hereI have to find number of hrs when machines operating are increased from 4 to 5. Simple logic says if I increase the no of machines, the no of hrs to complete the same work will be reduced. Hence if I have initial no. of hrs defined, I need to multiply it by proper fraction ie numerator/denominator < 1 Using above steps: No of hrs = 30 (when 4 machines are operational) I need to multiply this by 4/5 since I need a fraction less than 1. Hence I get 30 * (4/5) = 24 as hrs required when 5 machines are operational. I already know that when 4 machines are working, I shall need 30 hrs. Hence, difference = 3024 ie 6 hrs.
_________________
It's the journey that brings us happiness not the destination.



Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 8281
Location: Pune, India

Re: Five machines at a certain factory operate at the same constant rate
[#permalink]
Show Tags
20 May 2018, 20:38
adkikani wrote: Hi VeritasPrepKarishma chetan2u niks18 gmatbusters BunuelLet me know if my below approach is correct using 'Joint variation' as discussed hereI have to find number of hrs when machines operating are increased from 4 to 5. Simple logic says if I increase the no of machines, the no of hrs to complete the same work will be reduced. Hence if I have initial no. of hrs defined, I need to multiply it by proper fraction ie numerator/denominator < 1 Using above steps: No of hrs = 30 (when 4 machines are operational) I need to multiply this by 4/5 since I need a fraction less than 1. Hence I get 30 * (4/5) = 24 as hrs required when 5 machines are operational. I already know that when 4 machines are working, I shall need 30 hrs. Hence, difference = 3024 ie 6 hrs. Yes, absolutely correct.
_________________
Karishma Veritas Prep GMAT Instructor
Learn more about how Veritas Prep can help you achieve a great GMAT score by checking out their GMAT Prep Options >
GMAT selfstudy has never been more personalized or more fun. Try ORION Free!



Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 3518
Location: United States (CA)

Re: Five machines at a certain factory operate at the same constant rate
[#permalink]
Show Tags
22 May 2018, 17:42
nalinnair wrote: Five machines at a certain factory operate at the same constant rate. If four of these machines, operating simultaneously, take 30 hours to fill a certain production order, how many fewer hours does it take all five machines, operating simultaneously, to fill the same production order?
(A) 3 (B) 5 (C) 6 (D) 16 (E) 24 The rate of 4 machines is 1/30. We can let the rate of 5 machines be n and create the equation: 4/(1/30) = 5/n 120 = 5/n 120n = 5 n = 5/120 = 1/24 So it will take 1/(1/24) = 24 hours for the 5 machines to fill the same order and thus it takes 6 fewer hours than if the order were filled by 4 machines. Answer: C
_________________
Scott WoodburyStewart
Founder and CEO
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions



Manager
Joined: 20 Jul 2018
Posts: 91
GPA: 2.87

Re: Five machines at a certain factory operate at the same constant rate
[#permalink]
Show Tags
19 Aug 2018, 21:24
Rate if 4 machines 1/30 Rate of 1 machine = 1/(30*4) Rate of 5 machines = 1*5/(30*4) = 1/24 So 5 machines complete work in 24 hourse and take 6 fewer hours. Answer is C Posted from my mobile device
_________________
Hasnain Afzal
"When you wanna succeed as bad as you wanna breathe, then you will be successful." Eric Thomas




Re: Five machines at a certain factory operate at the same constant rate &nbs
[#permalink]
19 Aug 2018, 21:24






