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A closed cylindrical tank contains 36pi cubic feet of water [#permalink]
 14 Jun 2012, 02:54
Question Stats:
60% (01:58) correct
39% (01:29) wrong based on 5 sessions
The Official Guide for GMAT® Review, 13th Edition - Quantitative Questions ProjectA closed cylindrical tank contains 36pi 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 Notice that some editions of OG have a typo saying that the height of the water in the tank is 2 feet, it should read "the height of the water in the tank is 4 feet".Diagnostic Test
Question: 5
Page: 20
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Re: A closed cylindrical tank contains 36pi cubic feet of water [#permalink]
14 Jun 2012, 02:54
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SOLUTIONNotice that some editions of OG have a typo saying that the height of the water in the tank is 2 feet, it should read "the height of the water in the tank is 4 feet".A closed cylindrical tank contains 36pi 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 Look at the diagram below:  Since the tank is half full when placed upright then naturally it'll also be half full when placed on its side, so the level of the water (when placed that way) will be half of the diameter, so r. Now, given that V_{water}=\pi{*r^2}*H_{water} --> 36\pi=\pi{r^2}*4 --> r=3. Answer: B.
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Re: A closed cylindrical tank contains 36pi cubic feet of water [#permalink]
14 Jun 2012, 07:24
when tank is placed on its side on level ground, hieght = radius of cylinder
radius will be ,
1/2 πr^2h = 36π
r=6
Answer - D
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Re: A closed cylindrical tank contains 36pi cubic feet of water [#permalink]
14 Jun 2012, 10:43
Bunuel, I think there is some error in the question as none of the answer choices are correct.
Here is my approach:
Volume of water = π(r^2)h = 2π(r^2) = 36π - As height of water is 2 feet
=> r^2 = 18
=> r = sqrt(18)
As the tank is regular shaped, the water level will be half of its height irrespective of the position of the cylinder. So when its lying flat, height of water will be half of diameter = radius = r = sqrt(18)
None of the answer choices has this, so it should either be sqrt(36) or sqrt (9) - I think the problem might have a problem!
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Re: A closed cylindrical tank contains 36pi cubic feet of water [#permalink]
14 Jun 2012, 11:11
Volume of water inside cylinder = 36pi = pir^2h
Here water is filled up to a height of 2 feet, so h=2
r^2 = 18
r=3 sqrt2
There might be a mistake in the given problem.
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Re: A closed cylindrical tank contains 36pi cubic feet of water [#permalink]
16 Jun 2012, 03:56
gnan wrote: Volume of water inside cylinder = 36pi = pir^2h
Here water is filled up to a height of 2 feet, so h=2
r^2 = 18
r=3 sqrt2
There might be a mistake in the given problem. I agree to your comment partially, in my opinion this question has some ambiguity when it states that the tank contains 36pi cubic feet of water and is filled to half its capacity, so we may assume that 36pi is the volume when half capacity. So it would be better to state that the tank, when full, can be filled with 36pi or the full capacity of the tank is 36pi, or something alike. But i think this is one of the small tricks of GMAT. But anyway if you solved this way and did not come up with answer you should see what else GMAT could think by saying 36pi, then you see that only possible answer is 3 (B)
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Re: A closed cylindrical tank contains 36pi cubic feet of water [#permalink]
16 Jun 2012, 04:13
Tricky. 650+ level. Volume of the Cylinder: pi*r^2*h= 36pi r^2*2=36 r^2=18 r=Sq root 18 Something wrong with the answer choices. This question is similar to one in OG12 except the height given is 4 feet there. Answer choices given are same.
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Re: A closed cylindrical tank contains 36pi cubic feet of water [#permalink]
22 Jun 2012, 03:02
SOLUTIONNotice that some editions of OG have a typo saying that the height of the water in the tank is 2 feet, it should read "the height of the water in the tank is 4 feet".A closed cylindrical tank contains 36pi 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 Look at the diagram below: Attachment: 
Cylinder.PNG [ 14.91 KiB | Viewed 3443 times ]
Since the tank is half full when placed upright then naturally it'll also be half full when placed on its side, so the level of the water (when placed that way) will be half of the diameter, so r. Now, given that V_{water}=\pi{*r^2}*H_{water} --> 36\pi=\pi{r^2}*4 --> r=3. Answer: B.
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RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory
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PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. NEW!!!
DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set. NEW!!!
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Re: A closed cylindrical tank contains 36pi cubic feet of water [#permalink]
28 Oct 2012, 00:29
p.s. for anyone still coming across this question and confused... If you're getting 3*sqrt(2) as the answer, you're reading a version of the book with the error mentioned in original post.
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Re: A closed cylindrical tank contains 36pi cubic feet of water
[#permalink]
28 Oct 2012, 00:29
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