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# When a cylindrical tank is filled with water at a rate

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GRE Instructor
Joined: 10 Apr 2015
Posts: 2311
Followers: 72

Kudos [?]: 2200 [1] , given: 27

When a cylindrical tank is filled with water at a rate [#permalink]  02 Feb 2019, 06:39
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Question Stats:

80% (02:04) correct 20% (03:23) wrong based on 5 sessions
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. $$\frac{\sqrt{10}}{2}$$

B. $$\sqrt{10}$$

C. $$4$$

D. $$5$$

E. $$10$$
[Reveal] Spoiler: OA

_________________

Brent Hanneson – Creator of greenlighttestprep.com

Last edited by Carcass on 02 Feb 2019, 07:42, edited 1 time in total.
GRE Instructor
Joined: 10 Apr 2015
Posts: 2311
Followers: 72

Kudos [?]: 2200 [1] , given: 27

Re: When a cylindrical tank is filled with water at a rate [#permalink]  04 Feb 2019, 08:31
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Expert's post
GreenlightTestPrep 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. $$\frac{\sqrt{10}}{2}$$

B. $$\sqrt{10}$$

C. $$4$$

D. $$5$$

E. $$10$$

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.

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

So, we get: 22 ≈ (2.2)(radius²)
Divide both sides by 2.2: 10 ≈ radius²

Cheers,
Brent
_________________

Brent Hanneson – Creator of greenlighttestprep.com

Re: When a cylindrical tank is filled with water at a rate   [#permalink] 04 Feb 2019, 08:31
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