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GMAT Prep - Mixtures

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bubbliiiiiiii GMAT Destroyer!
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GMAT Prep - Mixtures Post Fri Aug 12, 2011 3:22 am
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  • Lap #[LAPCOUNT] ([LAPTIME])
    Is the answer A?

    Please share your approach.
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    Post Fri Aug 12, 2011 3:53 am
    IMO A

    Here's my approach :

    From the statement, we can infer that
    10%x + 2%y = 5%z => .1x + .02y = .5z

    but, also, from the mixture, x+y = z
    hence, the equation becomes,
    .1x +.02y = .5(x+y)...we need values of x or y to get the other variable.

    (A) gives values of y. Hence, we can find out the value of X..sufficient
    (B) gives value of z..whcih is value of x+y..hence, insufficient.

    My ans : A

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    pemdas GMAT Titan Default Avatar
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    Post Fri Aug 12, 2011 3:58 am
    i don't think it's a
    don't apply alligation or other means of mechanical calc
    i would take algebraic translation solution for good ==> x/10 + y/50 = z/20
    we need to know both y and z for x

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    pemdas GMAT Titan Default Avatar
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    Post Fri Aug 12, 2011 4:00 am
    you say 10%x + 2%y = 5%z then you say 100%x + 100%y = 100%z ?

    krishnasty wrote:
    IMO A

    Here's my approach :

    From the statement, we can infer that
    10%x + 2%y = 5%z => .1x + .02y = .5z

    but, also, from the mixture, x+y = z
    hence, the equation becomes,
    .1x +.02y = .5(x+y)...we need values of x or y to get the other variable.

    (A) gives values of y. Hence, we can find out the value of X..sufficient
    (B) gives value of z..whcih is value of x+y..hence, insufficient.

    My ans : A

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    krishnasty Really wants to Beat The GMAT!
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    Post Fri Aug 12, 2011 4:10 am
    No, thats what i meant to say...
    when i say 10%x, i mean the amount of gravel G.
    Consider it this way:
    1 Liter drink contains 300ml flavour and 700ml soda. it is mixed with 2 Liter drink which contains 400ml of flavour and 600 ml of soda. This produces 1+2 =3 liter of drink. but the amount of flavour and soda are different.correct??

    pemdas wrote:
    you say 10%x + 2%y = 5%z then you say 100%x + 100%y = 100%z ?

    krishnasty wrote:
    IMO A

    Here's my approach :

    From the statement, we can infer that
    10%x + 2%y = 5%z => .1x + .02y = .5z

    but, also, from the mixture, x+y = z
    hence, the equation becomes,
    .1x +.02y = .5(x+y)...we need values of x or y to get the other variable.

    (A) gives values of y. Hence, we can find out the value of X..sufficient
    (B) gives value of z..whcih is value of x+y..hence, insufficient.

    My ans : A

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    Post Fri Aug 12, 2011 4:55 am
    Quote:
    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
    This is a weighted average question: X and Y are being combined to form Z.
    We can use alligation, which dictates the following:

    The proportion of each element in the mixture is the distance between the percentage attributed to the other element in the mixture and the percentage attributed to the mixture.

    Proportion of X = |Percent in Y - Percent in Z| = |2-5| = 3.
    Proportion of Y = |Percent in X - Percent in Z| = |10-5| = 5.
    X:Y = 3:5.
    Since 3+5 = 8, we know that X = 3/8 of the mixture.
    Thus, X = (3/8)Z.

    Statement 1: Y=10.
    Since X:Y = 3:5 = 6:10, X=6.
    Sufficient.

    Statement 2: Z=16.
    Thus, X = (3/8)*16 = 6.
    Sufficient.

    The correct answer is D.

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    amit.trivedi@ymail.com GMAT Destroyer!
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    Post Tue Mar 13, 2012 7:05 am
    very good explanation given by GMATGuru...

    Thank You...

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