Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Working simultaneously at their respective constant rates, M [#permalink]
06 Dec 2012, 08:58

00:00

A

B

C

D

E

Difficulty:

35% (medium)

Question Stats:

65% (02:26) correct
34% (01:45) wrong based on 282 sessions

Working simultaneously at their respective constant rates, Machines A and B produce 800 nails in x hours. Working alone at its constant rate, Machine A produces 800 nails in y hours. In terms of x and y, how many hours does it take Machine B, working alone at its constant rate, to produce 800 nails?

Re: Working simultaneously at their respective constant rates, M [#permalink]
06 Dec 2012, 11:28

8

This post received KUDOS

Walkabout wrote:

Working simultaneously at their respective constant rates, Machines A and B produce 800 nails in x hours. Working alone at its constant rate, Machine A produces 800 nails in y hours. In terms of x and y, how many hours does it take Machine B, working alone at its constant rate, to produce 800 nails?

Re: Working simultaneously at their respective constant rates, M [#permalink]
06 Dec 2012, 09:06

2

This post received KUDOS

Expert's post

Walkabout wrote:

Working simultaneously at their respective constant rates, Machines A and B produce 800 nails in x hours. Working alone at its constant rate, Machine A produces 800 nails in y hours. In terms of x and y, how many hours does it take Machine B, working alone at its constant rate, to produce 800 nails?

Say x=1 hour and y=2 hours (notice that y must be greater than x, since the time for machine A to do the job, which is y hours, must be more than the time for machines A and B working together to do the same job, which is x hours).

In this case, the time needed for machine B to do the job must also be 2 hours: 1/2+1/2=1.

Now, plug x=1 and y=2 in the options to see which one yields 2. Only option E fits.

Re: Working simultaneously at their respective constant rates, M [#permalink]
04 Oct 2013, 07:31

Jp27 wrote:

Walkabout wrote:

Working simultaneously at their respective constant rates, Machines A and B produce 800 nails in x hours. Working alone at its constant rate, Machine A produces 800 nails in y hours. In terms of x and y, how many hours does it take Machine B, working alone at its constant rate, to produce 800 nails?

The above sol is awesome.... but i did it the longer way, algebraically...

rate of A be a and B be b

a + b = 800/x ..... 1 a = 800/y ..... 2

Use 2 in 1... we get

b = 800 (y-x) / xy

Finally

Rate of B * time = Work done by B (we want time)

800 (y-x) / xy * t = 800

t = xy / (y-x)

Yeah, R*T=W is a lengthy way to solve these problems but, I have seen that it is almost a sure shot way to solve most of the problems on this concept. Picking up the smart numbers may be a neat way to solve these questions but it highly depends on the mental state when you are taking the exam.
_________________

--------------------------------------------------------------- Consider to give me kudos if my post helped you.

Re: Working simultaneously at their respective constant rates, M [#permalink]
02 Nov 2013, 07:20

Jp27 wrote:

Walkabout wrote:

Working simultaneously at their respective constant rates, Machines A and B produce 800 nails in x hours. Working alone at its constant rate, Machine A produces 800 nails in y hours. In terms of x and y, how many hours does it take Machine B, working alone at its constant rate, to produce 800 nails?

Re: Working simultaneously at their respective constant rates, M [#permalink]
03 Nov 2013, 10:27

Expert's post

ronr34 wrote:

Jp27 wrote:

Walkabout wrote:

Working simultaneously at their respective constant rates, Machines A and B produce 800 nails in x hours. Working alone at its constant rate, Machine A produces 800 nails in y hours. In terms of x and y, how many hours does it take Machine B, working alone at its constant rate, to produce 800 nails?

Re: Working simultaneously at their respective constant rates, M [#permalink]
17 Nov 2013, 01:11

Simplest solution Here-

RA + RB = 1/X

RA = 1/Y

RB = (1/X - 1/Y) = (Y-X)/XY

Time = 1/RB = XY/(X+Y)

I have treated 800 as equivalent to unity(= 1), as it's presence in final answer was trivial, as it will eventually cancel out, taking it unity has make the solution quite Un Complex..
_________________

Re: Working simultaneously at their respective constant rates, M [#permalink]
06 Apr 2014, 15:49

I managed to solve this via plugging in numbers but I went over 3 minutes! With these plug-in-numbers type of problems, I strive to pick simple numbers but there always seems to be one, usually the one i'm solving for, that ends up being a rather complicated number. My question is:

1) I plugged in Rate A and Rate A+B and then solved for time. Should I have plugged in numbers for time directly. Is there a general rule as to what number I should be plugging in? 2) In this case, to keep things super simple, I could have plugged the total Rate to be 8 and Ra and Rb to both be 4. Is it bad practice to choose the same numbers for the individual rates/times?

Re: Working simultaneously at their respective constant rates, M [#permalink]
07 Apr 2014, 00:04

russ9 wrote:

I managed to solve this via plugging in numbers but I went over 3 minutes! With these plug-in-numbers type of problems, I strive to pick simple numbers but there always seems to be one, usually the one i'm solving for, that ends up being a rather complicated number. My question is:

1) I plugged in Rate A and Rate A+B and then solved for time. Should I have plugged in numbers for time directly. Is there a general rule as to what number I should be plugging in? 2) In this case, to keep things super simple, I could have plugged the total Rate to be 8 and Ra and Rb to both be 4. Is it bad practice to choose the same numbers for the individual rates/times?

Just refer to method of Bunuel; he did using plug-ins.

I used same variables available & got correct answer (Had taken 800 = 1 as done by honchos)
_________________

Kindly press "Kudos" to express appreciation

gmatclubot

Re: Working simultaneously at their respective constant rates, M
[#permalink]
07 Apr 2014, 00:04