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Cylinder of water

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Cylinder of water

by sanaa.rizwan » Tue May 14, 2013 12:17 pm
When a cylindrical tank is filled with water at a rate of 22 cubic meters per hour, the level of water in the tank rises at a rate of 0.7 meters per hour. Which of the following best approximates the radius of the tank in meters?

a.4
b.5
c.10
d. underoot 10
e. underoot 10/2
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by srcc25anu » Tue May 14, 2013 1:01 pm
Ht in 1 hour = 0.7 mts
Volume filled in 1 hour = πr^2h = 22 cubic mts
r^2 = 22 / (0.7*Ï€) = 10 sq mts
R = √10 mts

Ans D
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by Brent@GMATPrepNow » Tue May 14, 2013 1:08 pm
sanaa.rizwan wrote:When a cylindrical tank is filled with water at a rate of 22 cubic meters per hour, the level of water in the tank rises at a rate of 0.7 meters per hour. Which of the following best approximates the radius of the tank in meters?

a.4
b.5
c.10
d. underoot 10
e. underoot 10/2
Let's examine what occurs in a 1-hour period
The volume of water increases by 22 cubic meters.
The height of the water increases by 0.7 meters.

So, we need to find the radius of a 0.7 meter high cylinder that has a volume of 22 cubic meters.

Volume = (pi)r²h
22 = (pi)r²(0.7)

IMPORTANT: notice that (pi)(0.7) = approximately 2.2

So, we get: 22 = (2.2)r²
Divide both sides by 2.2: 10 = r²
Solve: r = √10 (approximately)

Answer: D

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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