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A contractor combined x tons of a gravel mixture that contained 10 per
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Updated on: 11 Jun 2019, 04:06

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

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28 Jan 2010, 16:25

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37

ugimba wrote:

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

(1) y = 10

(2) z = 16

Set the equation: \(0.1x+0.02y=0.05(x+y)\), where \(x+y=z\) --> \(5x=3y\) --> Q: \(x=?\)

Re: A contractor combined x tons of a gravel mixture that contained 10 per
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15 Jun 2010, 05:53

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What does the prompt tell us?

x + y = z

0.1x + 0.02y = 0.05z

We have to find x. If you notice, we have two equations in 3 variables, so if we are given a value for either y OR z, this is sufficient to calculate x.

Re: A contractor combined x tons of a gravel mixture that contained 10 per
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16 Aug 2010, 00:34

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lalithajob wrote:

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?

1. y = 10 2. z = 16

x + y = z ( x tons of mixture1 + y tons of mixture2 = z tons of combined mixture) .1x + .02y = .05z (gravel in mixture1 + gravel in mixture2 = gravel in combined mixture)

x= ?

1) y=10. 3 equations(2 from the question + 1 from answer choice) with 3 unknowns. Can solve for x. Sufficient 2) z=16. 3 equations(2 from the question + 1 from answer choice) with 3 unknowns. Can solve for x. Sufficient

Answer D
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Re: A contractor combined x tons of a gravel mixture that contained 10 per
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26 Dec 2010, 23:06

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anilnandyala wrote:

a contractor combined x tons ofa 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 by weight. what is the value of x?

y = 10 z = 16

Using scale method here, since 10% and 2% give weighted average of 5%, x:y = 3:5 We also know x + y = z.

1. y = 10. If y = 10, x = 6 since their ratios must be 3:5. Sufficient.

2. z = 16 If sum of x and y is 16, x must be 6 and y must be 10 to give a ratio of 3:5.

If this is not intuitive, think of it this way: x : y...... x + y 3 : 5...... 8 Since 8 in ratio terms is actually 16, 3 is actually 6 and 5 is actually 10.

Answer (D)

It will be worth your while if you understand the scale method. The time saving is huge and weighted average is a concept you will need to use time and again. For explanation of scale method, check this link: http://gmatclub.com/forum/tough-ds-105651.html#p828579 _________________

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 >

Re: A contractor combined x tons of a gravel mixture that contained 10 per
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12 Mar 2011, 23:38

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The answer is D. I was flummoxed on this one since at first I thought it was C, then I looked at it closer and thought it was B. Now I see how A and B are sufficient. Crazy DS - I HATE YOU!

Re: A contractor combined x tons of a gravel mixture that contained 10 per
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15 Apr 2012, 16:40

ad20 wrote:

Can anyone please explain on X+Y=Z in que statement. I definitely missed it and ended up with answer C Where in question it says that x+y=z?

Sure. Question says: "A contractor combined x tons of a gravel mixture that contained 10 percent gravel G, by weight, with y tons of a mixture that contained 2 percent gravel G, by weight, to produce z tons of a mixture."

Re: A contractor combined x tons of a gravel mixture that contained 10 per
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14 Jan 2016, 11:16

ugimba wrote:

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

(1) y = 10

(2) z = 16

It's a weighted average problem. X(10)....5....5.....3.....Y(2) \(\frac{x}{y}=\frac{3}{5}\)

Re: A contractor combined x tons of a gravel mixture that contained 10 per
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14 Jan 2016, 18:34

Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

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

(1) y = 10

(2) z = 16

When you modify the original condition and the question, they becomes x+y=z and (10/100)x+(2/100)y=(5/100)z, 10x+2y=5z. Then there are 3 variables(x,y,z) and 2 equations, which should match with the number of equations. So you need 1 more equation. For 1) 1 equation, for 2) 1 equation, which is likely to make D the answer. For 1), when y=10, x+y=z, 10x+2y=5z → x+10=z, 10x+20=z. Since the value of x is unique, it is sufficient. For 2), when z=16, the value of x is also unique in x+y=16, 10x+2y=80, which is unique and sufficient. Therefore, the answer is D.

For cases where we need 1 more equation, such as original conditions with “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.
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Re: A contractor combined x tons of a gravel mixture that contained 10 per
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28 Jan 2017, 15:44

x = 10% gravel y = 2% gravel. z = the MIXTURE of x and y = 5% gravel.

To determine the required ratio of x to y, use ALLIGATION -- a very efficient way to handle MIXTURE PROBLEMS.

Step 1: Plot the 3 percentages on a number line, with the percentages for x and y on the ends and the percentage for mixture z in the middle. x 10%-----------5%-----------2% y

Step 2: Calculate the distances between the percentages. x 10%-----5-----5%----3-----2% y

Step 3: Determine the ratio in the mixture. The required ratio of x to y is equal to the RECIPROCAL of the distances in red. x:y = 3:5.

Since x:y = 3:5, and 3+5 = 8, every 8 tons of mixture z is composed of 3 tons of x and 5 tons of y.

Re: A contractor combined x tons of a gravel mixture that contained 10 per
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04 Aug 2018, 08:38

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Top Contributor

ugimba wrote:

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

(1) y = 10

(2) z = 16

Let's use some weighted averages to solve this question Weighted average of groups combined = (group A proportion)(group A average) + (group B proportion)(group B average) + (group C proportion)(group C average) + ...

Target question:What is the value of x ?

Given: A contractor combined x tons of a gravel mixture that contained 10 percent gravel G, by weight, with y tons of a mixture that contained 2 percent gravel G, by weight, to produce z tons of a mixture that was 5 percent gravel G, by weight. First, we can write: x + y = z

Also, the total weight of the mixture = z (aka x + y) So, when we apply the above formula, we get: 5% = (x/z)(10%) + (y/z)(2%) Ignore the % symbols: 5 = (x/z)(10) + (y/z)(2) Multiply both sides by z to get: 5z = 10x + 2y Since x + y = z, we can rewrite the above equation as: 5(x +y) = 10x + 2y Expand: 5x + 5y = 10x + 2y Simplify to get: 5x - 3y = 0

Now onto the statements!!!!!

Statement 1: y = 10 Replace y with 10 to get: 5x - 3(10) = 0 Solve to get, x = 6 Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: z = 16 In other words, x + y = 16

So, we have: 5x - 3y = 0 and x + y = 16 Since we have 2 linear equations with 2 variables, we COULD solve the system for x, which means we COULD answer the target question So, statement 2 is SUFFICIENT

Re: A contractor combined x tons of a gravel mixture that contained 10 per
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16 Apr 2019, 12:01

ugimba wrote:

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

(1) y = 10

(2) z = 16

Here's a visual graph for this question. This means 2 things: There's more 2% gravel than 10% The ratio of 2%/10% mixture is 5/3

Now if we know the values of x, y and z, we will get a sufficient answer.

Both Statement 1 and 2 gives one of those variables, so the answer is D