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.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 350,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

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:

A contractor combined -GMATPrep [#permalink]
30 Jan 2009, 11:10

A contractor combined x tons of a gravel mixture that contained 10% gravel G, by weight, with y tons of a mixture that contained 2% gravel G, by weight, to produce z tons of a mixture that was 5% gravel G, by weight. What is the value of x?

Re: A contractor combined -GMATPrep [#permalink]
30 Jan 2009, 11:27

IMO D.

here is my approach.

It is given that 0.1x + 0.02y = 0.05z. Eq-----> Eq1 Also x + y = z ----> Eq 2

Two eqautions and 3 unknowns. To solve for x, we need to have atleast 3 distinct linear equations.

Stmt1---> y = 10. from this we have 3 equations two from the question stem and third from the statment. Three equations and 3 unknowns. Sifficient. Stmt2 ---> z = 16 from this we have 3 equations two from the question stem and third from the statment. Three equations and 3 unknowns. Sifficient.

Hence D is the ans.

Last edited by mrsmarthi on 30 Jan 2009, 12:46, edited 1 time in total.

Re: A contractor combined -GMATPrep [#permalink]
30 Jan 2009, 11:50

2

This post received KUDOS

Expert's post

D

This is a C-trap.

1. Fast 10sec approach (if we don't have enough time):

- if we have two mixtures with different % and prepare a new mixture, it is obvious that final % will depend only on ratio between two start mixtures. Therefore, if we know all % and weight of any mixture (z or y), we can find x.

2. Usual approach.

We have system of equations: 0.1x+0.02y=0.05z x+y=z

Now, we can write out the system separately for two conditions and will get a system with two equations and two variables - each condition is sufficient:

Re: A contractor combined -GMATPrep [#permalink]
30 Jan 2009, 12:44

walker wrote:

D

This is a C-trap.

1. Fast 10sec approach (if we don't have enough time):

- if we have two mixtures with different % and prepare a new mixture, it is obvious that final % will depend only on ratio between two start mixtures. Therefore, if we know all % and weight of any mixture (z or y), we can find x.

2. Usual approach.

We have system of equations: 0.1x+0.02y=0.05z x+y=z

Now, we can write out the system separately for two conditions and will get a system with two equations and two variables - each condition is sufficient:

1) y=10 0.1x+0.2=0.05z x+10=z

x=6

2) z=16 0.1x+0.02y=0.8 x+y=16

x=6

Rightly said. And looks obvoise that that I am frequent victim of that trap w.r.t DS. BTW, I have corrected my previous post. I missed that x + y = z fact.

Re: A contractor combined -GMATPrep [#permalink]
31 Jan 2009, 12:24

walker wrote:

D

This is a C-trap.

1. Fast 10sec approach (if we don't have enough time):

- if we have two mixtures with different % and prepare a new mixture, it is obvious that final % will depend only on ratio between two start mixtures. Therefore, if we know all % and weight of any mixture (z or y), we can find x.

2. Usual approach.

We have system of equations: 0.1x+0.02y=0.05z x+y=z

Now, we can write out the system separately for two conditions and will get a system with two equations and two variables - each condition is sufficient:

1) y=10 0.1x+0.2=0.05z x+10=z

x=6

2) z=16 0.1x+0.02y=0.8 x+y=16

x=6

Hi walker,

can you explain me the 10 second approach in detail.

Re: A contractor combined -GMATPrep [#permalink]
31 Jan 2009, 13:43

Expert's post

Let's consider another similar situation: we have two paints, yellow and blue. In order to get green color we have to mix blue and yellow paints at a special ratio. For example, 1 liter of yellow paint and 2 liters of blue paint give us necessary green paint (1:2 ratio). In other words, we can get green paint only if we follow strictly the ratio, otherwise resulted paint will contain more blue or more yellow. In our example, if we have 20 litters of yellow paint, we should get 40 litters of blue paint, not more or less. If we make 60 litters of green paint, we should take 20 liters of yellow and 40 litters of blue.

The same reasoning in the problem. We know all concentrations. Therefore, we have a special ratio of initial mixtures in order to get resulted mixture. knowing amount only one mixture is enough to find others using the ration.

By the way, this problem 7-t75289 uses the same idea. So, you can solve it very quickly. _________________

How the growth of emerging markets will strain global finance : Emerging economies need access to capital (i.e., finance) in order to fund the projects necessary for...

One question I get a lot from prospective students is what to do in the summer before the MBA program. Like a lot of folks from non traditional backgrounds...