Can't understand this problem.....

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yumi2012: Senior | Next Rank: 100 Posts; Posts: 64; Joined: Mon Jul 23, 2012 1:59 pm; Thanked: 1 times

by yumi2012 » Tue Sep 03, 2013 6:19 pm

A closed cylindrical tank contains 36Ï€ cubic feet of water and is filled to half its capacity. When the tank is placed upright on its circular base on level ground, the height of the water in the tank is 4 feet. When the tank is placed on its side on level ground, what is the height, in feet, of the surface of the water above the ground?

(A) 2
(B) 3
(C) 4
(D) 6
(E) 9

Official guide question
-------

According to the answer guide, the answer is 3... which surprised me.. So the water in the tank was actually 18pai? And the 36 pai was just the capacity of the tank?

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Source: Beat The GMAT — Problem Solving | Tue Sep 03, 2013 6:19 pm

ganeshrkamath: Master | Next Rank: 500 Posts; Posts: 283; Joined: Sun Jun 23, 2013 11:56 pmFollowed by: 26 members; Location: Bangalore, India; Thanked: 97 times; GMAT Score:750

by ganeshrkamath » Tue Sep 03, 2013 7:58 pm

yumi2012 wrote:A closed cylindrical tank contains 36Ï€ cubic feet of water and is filled to half its capacity. When the tank is placed upright on its circular base on level ground, the height of the water in the tank is 4 feet. When the tank is placed on its side on level ground, what is the height, in feet, of the surface of the water above the ground?

(A) 2
(B) 3
(C) 4
(D) 6
(E) 9

Official guide question
-------

According to the answer guide, the answer is 3... which surprised me.. So the water in the tank was actually 18pai? And the 36 pai was just the capacity of the tank?

The question basically asks you to find the radius of the cylinder.
Volume = 36Ï€*2 = 72Ï€
Volume = Ï€ (r^2) h
h = 4*2 = 8

72Ï€ = 8 (r^2) Ï€
r^2 = 9
r = 3

Choose B

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GMAT Score: 750 V40 Q51 AWA 5 IR 8
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by [email protected] » Wed Sep 04, 2013 11:11 pm

Hi Yumi2012,

As you continue to practice, you'll find that many GMAT questions come with little hints (sometime Number Properties, sometimes patterns) that you can use to your advantage.

In this case, the prompt tells you that the cylinder is "half full"; this means that regardless of what "side" you lay the cylinder on, the water will go "half-way" up. When you lay the cylinder on its side, "half-way" would be the radius.

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

Contact Rich at [email protected]

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