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Might be really easy but couldn't figure it out

This topic has 1 expert reply and 2 member replies
imane81 Senior | Next Rank: 100 Posts Default Avatar
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Might be really easy but couldn't figure it out

Post Fri Jan 22, 2010 12:35 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    Thank for solving this one ..

    When n liters of fuel was added to a tank that was already 1/3 full, the tank was filled to 7/9 of its capacity. In terms of n, what is the capacity of the tank, in liters?
    A. 10/9n
    B. 4/3n
    C. 3/2n
    D. 9/4n
    E. 7/3n

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    ace_gre Senior | Next Rank: 100 Posts Default Avatar
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    Post Fri Jan 22, 2010 1:07 pm
    Hi, Here is my approach.

    Say the capacity of tank is T.

    n+ T/3 = 7T/9
    n = 7T/9 - T/3
    n= 4T/9
    T = 9n/4

    I am assuming that ns in the choices are in the numerator.

    thephoenix Legendary Member
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    Post Fri Jan 22, 2010 10:14 pm
    imane81 wrote:
    Thank for solving this one ..

    When n liters of fuel was added to a tank that was already 1/3 full, the tank was filled to 7/9 of its capacity. In terms of n, what is the capacity of the tank, in liters?
    A. 10/9n
    B. 4/3n
    C. 3/2n
    D. 9/4n
    E. 7/3n
    eqn is (1/3)x+n=(7/9)x
    solving for x=(9/4) n

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    Stuart Kovinsky GMAT Instructor
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    Post Sat Jan 23, 2010 1:05 am
    imane81 wrote:
    Thank for solving this one ..

    When n liters of fuel was added to a tank that was already 1/3 full, the tank was filled to 7/9 of its capacity. In terms of n, what is the capacity of the tank, in liters?
    A. 10/9n
    B. 4/3n
    C. 3/2n
    D. 9/4n
    E. 7/3n
    This is an ideal situation for picking numbers if the algebra doesn't leap out at you.

    We have 1/3 and 7/9, so let's set the capacity of the tank at 9 litres to keep the arithmetic simple.

    We started at 1/3 full: that's 3 litres.
    We ended at 7/9 full: that's 7 litres.

    Therefore, we added 4 litres, i.e. n=4.

    Since the question is asking for the capacity of the tank in terms of n, we want to pick the choice that gives us a value of 9 (the capacity of our tank) when we plug in n=4.

    a) 40/9... bzzt
    b) 16/3... bzzt
    c) 12/2... bzzt
    d) 36/4... ding ding - we have a winner!

    Since all the choices are simple multiples of n, no need to check (e).

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