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:

Machine A and machine B are each used to manufacture 660 [#permalink]
07 Aug 2010, 04:37

1

This post received KUDOS

3

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

65% (hard)

Question Stats:

59% (02:35) correct
41% (01:45) wrong based on 178 sessions

Machine A and machine B are each used to manufacture 660 sprockets. It takes machine A 10 hours longer to produce 660 sprockets than machine B. Machine B produces 10 percent more sprockets per hour than machine A. How many sprockets per hour does machine A produces?

Re: Kaplan "800" rate: Machines [#permalink]
07 Aug 2010, 05:04

3

This post received KUDOS

Expert's post

zisis wrote:

Machine A and machine B are each used to manufacture 660 sprockets. It takes machine A 10 hours longer to produce 660 sprockets than machine B. Machine B produces 10 percent more sprockets per hour than machine A. How many sprockets per hour does machine A produces?

6 6.6 60 100 110

book give a backsolving solution which I am not a big fan of...........please explain method...

Let time needed for machine A to produce 660 sprockets be a hours, then the rate of machine A would be rate_A=\frac{job \ done}{time}=\frac{660}{a} sprockets per hour;

As "it takes machine A 10 hours longer to produce 660 sprockets than machine B" then time needed for machine B to produce 660 sprockets be a-10 hours and the rate of machine B would be rate_B=\frac{job \ done}{time}=\frac{660}{a-10} sprockets per hour;

As "machine B produces 10 percent more sprockets per hour than machine A" then rate_A*1.1=rate_B --> \frac{660}{a}*1.1=\frac{660}{a-10} --> a=110 --> rate_A=\frac{job \ done}{time}=\frac{660}{a}=6.

Re: Kaplan "800" rate: Machines [#permalink]
13 Aug 2010, 06:21

Thanks very much for the solution and explanation, Bunuel. One quick clarification though. In the explanation you make the jump from (660/a)*1.1 = 660/(a-10) to a = 110. Can you give a quick explanation for how you made that jump?

Re: Kaplan "800" rate: Machines [#permalink]
13 Aug 2010, 06:28

1

This post received KUDOS

Expert's post

mrwuzzman wrote:

Thanks very much for the solution and explanation, Bunuel. One quick clarification though. In the explanation you make the jump from (660/a)*1.1 = 660/(a-10) to a = 110. Can you give a quick explanation for how you made that jump?

Re: Kaplan "800" rate: Machines [#permalink]
14 Aug 2010, 12:57

Expert's post

zisis wrote:

Machine A and machine B are each used to manufacture 660 sprockets. It takes machine A 10 hours longer to produce 660 sprockets than machine B. Machine B produces 10 percent more sprockets per hour than machine A. How many sprockets per hour does machine A produces?

6 6.6 60 100 110

book give a backsolving solution which I am not a big fan of...........please explain method...

Hi zisis,

Sorry you're not a fan of Kaplan's backsolving methods, but in this case it can be really helpful.

Here, a little estimation goes a long way. We know that A works 10 hours longer than B does, so if A is making 100 or 110 sprockets per hour, it would be making 1000+ sprockets--impossible! Even 60/hour is clearly too high

Given that, the correct answer has to be either A or B. So, we start where it's easiest--the whole number. If A makes 6 sprockets/hour, then A will take 110 hours to produce 660 sprockets. Meanwhile, if A makes 6 sprockets per hour and B makes 10% more, B must make 6.6 sprockets/hour. B would therefore take 100 hours to make 660 sprockets.

The question stem tells us that A should work 10 more hours than B. When we plug 6 back into the question, A does work 10 more hours than B--that confirms that A is the correct answer, with a minimum of crunchy math. _________________

Re: Kaplan "800" rate: Machines [#permalink]
14 Aug 2010, 14:16

KapTeacherEli wrote:

zisis wrote:

Machine A and machine B are each used to manufacture 660 sprockets. It takes machine A 10 hours longer to produce 660 sprockets than machine B. Machine B produces 10 percent more sprockets per hour than machine A. How many sprockets per hour does machine A produces?

6 6.6 60 100 110

book give a backsolving solution which I am not a big fan of...........please explain method...

Hi zisis,

Sorry you're not a fan of Kaplan's backsolving methods, but in this case it can be really helpful.

Here, a little estimation goes a long way. We know that A works 10 hours longer than B does, so if A is making 100 or 110 sprockets per hour, it would be making 1000+ sprockets--impossible! Even 60/hour is clearly too high

Given that, the correct answer has to be either A or B. So, we start where it's easiest--the whole number. If A makes 6 sprockets/hour, then A will take 110 hours to produce 660 sprockets. Meanwhile, if A makes 6 sprockets per hour and B makes 10% more, B must make 6.6 sprockets/hour. B would therefore take 100 hours to make 660 sprockets.

The question stem tells us that A should work 10 more hours than B. When we plug 6 back into the question, A does work 10 more hours than B--that confirms that A is the correct answer, with a minimum of crunchy math.

no offence......sometimes when i am stuck I will use backsolving but I try not to rely on it....

Re: Kaplan "800" rate: Machines [#permalink]
17 Dec 2011, 14:25

zisis wrote:

Machine A and machine B are each used to manufacture 660 sprockets. It takes machine A 10 hours longer to produce 660 sprockets than machine B. Machine B produces 10 percent more sprockets per hour than machine A. How many sprockets per hour does machine A produces?

6 6.6 60 100 110

book give a backsolving solution which I am not a big fan of...........please explain method...

If i form the following equation from the condition is it wrong? 660/x - 660/x+10 =10/100 _________________

Machine A and Machine B are each used to manufacture 660 sprockets. It takes machine A 10 hours longer to produce 660 sprockets than machine B. Machine B produces 10 percent more sprockets per hour than machine A. How many sprockets per hour does machine A produce.

a. 6 b. 6.6 c. 60 d. 100 e. 110

Source says - this is a very difficult rate problem hence choosing 700+. Please solve without back solving.

Suppose rate of B is b and rate of A is a. Suppose B takes x hours to produce 660 sprockets, so 660/b = x ( b = number of sprockets produced by B in one hour ) So A takes x + 10 hours to produce 660 sprockets or 660/a = x + 10. Now it is given that B produces 10% more sprockets than A in 1 hour, hence b = 110% of a or b = 1.1a 660/b = x and 660/a = x + 10 or 660/a - 10 = x From above, 660/b = 660/a - 10 ( since both of them equals x ) Since b = 1.1a 660/1.1a = 660/a - 10 Solving above equation will give us a = 6 sprockets/hour or we can say that A produces 6 sprockets per hour. Hence answer is option A

Re: Machine A and machine B are each used to manufacture 660 [#permalink]
04 Feb 2013, 09:41

Let 't' be the time.

Look at the attached RTW chart.

It is given Machine B produces 10% more per hour than machine, so the equation becomes-

\frac{660}{t} = \frac{660}{t+10}+\frac{66}{t+10}

This gives....> 66t=6600 Therefore t=100

Substituting t in rate of a... \frac{66}{t+10}gives the rate as 6.

Attachments

1.jpg [ 12.63 KiB | Viewed 2303 times ]

_________________

I've failed over and over and over again in my life and that is why I succeed--Michael Jordan Kudos drives a person to better himself every single time. So Pls give it generously Wont give up till i hit a 700+

Machine A and machine B are each used to manufacture 660 sprockets. It takes machine A 10 hours longer to produce 660 sprockets than machine B. Machine B produces 10 percent more sprockets per hour than machine A. How many sprockets per hour does machine A produces?

6 6.6 60 100 110

book give a backsolving solution which I am not a big fan of...........please explain method...

Let time needed for machine A to produce 660 sprockets be a hours, then the rate of machine A would be rate_A=\frac{job \ done}{time}=\frac{660}{a} sprockets per hour;

As "it takes machine A 10 hours longer to produce 660 sprockets than machine B" then time needed for machine B to produce 660 sprockets be a-10 hours and the rate of machine B would be rate_B=\frac{job \ done}{time}=\frac{660}{a-10} sprockets per hour;

As "machine B produces 10 percent more sprockets per hour than machine A" then rate_A*1.1=rate_B --> \frac{660}{a}*1.1=\frac{660}{a-10} --> a=110 --> rate_A=\frac{job \ done}{time}=\frac{660}{a}=6.

Answer: A.

Hope it's clear.

I did a similar approach, but what I did different was I said that Rate A = 660/(x+10) and Rate B = 1.1(660/x) This is basically saying B takes x hours and A takes x+10 hours.

Why is this wrong? Because I don't get the same answer.

Machine A and machine B are each used to manufacture 660 sprockets. It takes machine A 10 hours longer to produce 660 sprockets than machine B. Machine B produces 10 percent more sprockets per hour than machine A. How many sprockets per hour does machine A produces?

6 6.6 60 100 110

book give a backsolving solution which I am not a big fan of...........please explain method...

Let time needed for machine A to produce 660 sprockets be a hours, then the rate of machine A would be rate_A=\frac{job \ done}{time}=\frac{660}{a} sprockets per hour;

As "it takes machine A 10 hours longer to produce 660 sprockets than machine B" then time needed for machine B to produce 660 sprockets be a-10 hours and the rate of machine B would be rate_B=\frac{job \ done}{time}=\frac{660}{a-10} sprockets per hour;

As "machine B produces 10 percent more sprockets per hour than machine A" then rate_A*1.1=rate_B --> \frac{660}{a}*1.1=\frac{660}{a-10} --> a=110 --> rate_A=\frac{job \ done}{time}=\frac{660}{a}=6.

Answer: A.

Hope it's clear.

I did a similar approach, but what I did different was I said that Rate A = 660/(x+10) and Rate B = 1.1(660/x) This is basically saying B takes x hours and A takes x+10 hours. Why is this wrong? Because I don't get the same answer.

Thanks,

The highlighted part is not correct. Rate B = \frac{660}{x} and as Machine B makes more sprockets than Machine A, thus, by the given condition, Rate B = 1.1*Rate A.

Thus, \frac{660}{x} = 1.1*\frac{660}{(x+10)} = x+10 = 1.1x = x = 100. Thus, Per hour, Machine A would produce = \frac{660}{(100+10)} = \frac{660}{110)} = 6. _________________

Re: Machine A and machine B are each used to manufacture 660 [#permalink]
01 Aug 2013, 00:26

1. Let the number of sprockets produced by machine A in 1 hour be x 2. Number of sprockets produced by machine B in 1 hour is 1.1x

3. Let machine A take y hours to produce 660 sprockets. In 1 hour it produces 660/y sprockets 4. Machine B takes y-10 hours to produce 660 sprockets. In 1 hour it produces 660/y-10 sprockets

5. Equating (1) and (3) -> xy=660 6. Equating (2) and (4) -> 1.1xy-11x=660

Re: Machine A and machine B are each used to manufacture 660 [#permalink]
24 Dec 2013, 11:46

zisis wrote:

Machine A and machine B are each used to manufacture 660 sprockets. It takes machine A 10 hours longer to produce 660 sprockets than machine B. Machine B produces 10 percent more sprockets per hour than machine A. How many sprockets per hour does machine A produces?

A. 6 B. 6.6 C. 60 D. 100 E. 110

Let me chip in on this one

So we get that B manufactures the 660 sprockets in 10 hours less which indeed are 10%. Therefore total hours it takes is 100 Then A must take 10 hrs more hence 110 hours

Now, Total Work/Rate = 660/110 = 6 sprockets per hour

Answer is A Hope it helps Cheers! J

gmatclubot

Re: Machine A and machine B are each used to manufacture 660
[#permalink]
24 Dec 2013, 11:46