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Fractions problem - Platinum GMAT question

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by inertia2010 » Mon Jul 18, 2011 10:00 am
Please help on this on:

After installing a powerful pump onto a large gasoline tank, John pumped gasoline out of the tank. Each time John ran the pump, it removed 1/3 of the gas remaining in the tank. Assuming the gas tank was full when John began, what fraction of the total gas in the tank at the beginning was removed if John ran the pump three times?
A) 8/27
B) 1/27
C) 2/3
D) 19/27
E) 27/28

The answer is D.

Thanks!!
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Source: — Problem Solving |

by GMATGuruNY » Mon Jul 18, 2011 10:06 am
inertia2010 wrote:Please help on this on:

After installing a powerful pump onto a large gasoline tank, John pumped gasoline out of the tank. Each time John ran the pump, it removed 1/3 of the gas remaining in the tank. Assuming the gas tank was full when John began, what fraction of the total gas in the tank at the beginning was removed if John ran the pump three times?
A) 8/27
B) 1/27
C) 2/3
D) 19/27
E) 27/28
Let tank = 27 units.
First pump removes (1/3)*27 = 9 units.
Remaining units = 27-9 = 18.
Second pump removes (1/3)*18 = 6 units.
Remaining units = 18-6 = 12.
Third pump removes (1/3)*12 = 4 units.
Remaining units = 12-4 = 8.
Since only 8 units remain, total removed = 27-8 = 19.
Total removed/Tank = 19/27.

The correct answer is D.
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by inertia2010 » Mon Jul 18, 2011 2:07 pm
perfect explanation...thank you!!
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by KRISH1985 » Mon Jul 18, 2011 8:43 pm
Please block the answers, when you post a question. Like you have mentioned D just below the question. Thanks!
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