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## Might be really easy but couldn't figure it out

This topic has 2 expert replies and 2 member replies
imane81 Senior | Next Rank: 100 Posts
Joined
13 Jan 2010
Posted:
40 messages
1

#### Might be really easy but couldn't figure it out

Fri Jan 22, 2010 12:35 pm
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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Rich.C@EMPOWERgmat.com Elite Legendary Member
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Tue Mar 13, 2018 7:04 pm
Hi All,

We're told that 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. We're asked for the capacity of the tank, in terms of N, in liters. This question can be solved by TESTing VALUES.

Since the tank ends up 7/9 full, it would make sense to choose a value for the FULL TANK that is a multiple of 9. In this case, the easiest value would be 9 (note: this is NOT the value of N). We can now set up an equation and solve for N...

N + (1/3)(9) = (7/9)(9)
N + 3 = 7
N = 4

Thus, we're looking for an answer that equals 9 when N=4. There's only one answer that matches...

GMAT assassins aren't born, they're made,
Rich

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Stuart Kovinsky GMAT Instructor
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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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ace_gre Senior | Next Rank: 100 Posts
Joined
23 Nov 2009
Posted:
98 messages
26
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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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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