Working simultaneously

Expert replies

ska7945: Master | Next Rank: 500 Posts; Posts: 200; Joined: Thu Aug 07, 2008 5:14 pm; Thanked: 1 times

by ska7945 » Tue Sep 02, 2008 8:35 pm

Working simultaneously and independently at an identical constant rate, 4 machines of a certain type can produce a total of x units of product P in 6 days. How many of these machines, working simultaneously and independently at this constant rate, can produce a total of 3x units of product P in 4 days?

A. 24
B. 18
C. 16
D. 12
E. 8

oa B

let's beat GMAT.

Like this post

Source: Beat The GMAT — Problem Solving | Tue Sep 02, 2008 8:35 pm

mehravikas: Legendary Member; Posts: 1161; Joined: Mon May 12, 2008 2:52 amFollowed by: 1 member; Location: Sydney; Thanked: 23 times

by mehravikas » Tue Sep 02, 2008 9:41 pm

Plug in numbers for this problem.

Let x = 24

therefore, 4 machines produce 24 units in 6 days, that gives us 4 units per day for 6 days.

Case 1 -
Machines -> 4, Units -> 24, Days -> 6

Case 2 -
Machines -> M, Units -> 72 (remember 3x), Days -> 4

M = 72 / 4 -> M = 18

18 machines can produce 72 units in 4 days.

Last edited by mehravikas on Tue Sep 02, 2008 10:08 pm, edited 1 time in total.

Like this post

P_mashru: Senior | Next Rank: 100 Posts; Posts: 43; Joined: Wed Jun 11, 2008 5:03 am; Location: Mumbai; GMAT Score:530

by P_mashru » Tue Sep 02, 2008 9:51 pm

Total work by 4 machines in 1 day - (1/6 + 1/6 + 1/6 + 1/6) x = 2/3 x

total work to be done - 3x, by 4 machines in 1 day = 9x /2x = 4.5 units

no of machines reuqured to do 3x work in 4 days = 4.5 x 4 = 18

I am I

Like this post

caloga: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Thu Sep 04, 2008 8:15 am

Re: Working simultaneously

by caloga » Sat Sep 06, 2008 1:21 am

4 machines--x units--6 days

4 machines--how many units?--4 days

how many units=y

y=4x/6=2x/3

how many machines--3x units--4 days

how many machines=z

z=12x/y=12x/(2x/3)=18

Like this post

kshankker: Senior | Next Rank: 100 Posts; Posts: 30; Joined: Fri Jul 04, 2008 5:28 am; Thanked: 1 times

by kshankker » Sat Sep 06, 2008 8:05 am

Hey this problem takes only 45 sec. Formula : amount = rate * work done
Given R1=R2:

step 1 : X= R1 * (4Machines * 6 days)
step 2 : 3X = R2* ( Y machines * 4 days )
step 3 : equate R1= R2
ie.. X/(4*6) = 3X/ (Y * 4)
Y = 18...

Hope you got it...........

Like this post

sumithshah: Master | Next Rank: 500 Posts; Posts: 165; Joined: Wed May 28, 2008 11:25 pm; Thanked: 9 times; GMAT Score:730

by sumithshah » Sat Sep 06, 2008 11:17 am

Simpler way ( I think )

4 machines do some work in 6 days
1 machine does it in 24 days.

24 days are needed to do some work by 1 machine
To do it in 4 days, we shall need : 6 machines.

To do thrice the work in 4 days, we shall need 18 machines.

I think the part where x and 3c comes in ( adding the 3rd variable ) simply kicks us in the head and confuses us. Essentially, its the same rate/work problems we've been doing in our heads all day long

Like this post

Jeff@TargetTestPrep: GMAT Instructor; Posts: 1462; Joined: Thu Apr 09, 2015 9:34 amFollowed by: 22 members; Location: New York, NY; Thanked: 39 times

by Jeff@TargetTestPrep » Mon Dec 11, 2017 5:25 pm

ska7945 wrote:Working simultaneously and independently at an identical constant rate, 4 machines of a certain type can produce a total of x units of product P in 6 days. How many of these machines, working simultaneously and independently at this constant rate, can produce a total of 3x units of product P in 4 days?

A. 24
B. 18
C. 16
D. 12
E. 8

We are given that 4 machines can complete x units in 6 days. Thus, the rate of the 4 machines is x/6.
Next we need to determine the number of machines needed to produce a rate of 3x/4. To calculate that number of machines, we can use the following proportion in which the value in each numerator is the number of machines and the value in each denominator is the corresponding rate of those machines. We can let n = the number of machines needed:

4/(x/6) = n/(3x/4)

24/x = 4n/3x

72x = 4nx

18 = n

Answer: B

Jeffrey Miller
Head of GMAT Instruction
[email protected]

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review