Geometry Volume

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Geometry Volume

by datonman » Sun Nov 01, 2015 9:50 pm
A closed cylindrical tank contains 36(pie) 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
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by GMATGuruNY » Mon Nov 02, 2015 2:57 am
datonman wrote:A closed cylindrical tank contains 36(pie) 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
Volume of the water = 36Ï€.
Height of the water = 4 feet.
Since V = πr²h, we get:
36π = π(r²)(4)
9 = r²
r = 3.
Thus, the radius of the cylinder is 3 feet.

The water constitutes HALF the cylinder.
Implication:
When the tank is placed on its side, the water will rise HALFWAY up the base of the cylinder, as illustrated here:
https://www.physicsforums.com/threads/h ... me.206625/
Since halfway up the base of the cylinder is equal to the RADIUS of the cylinder, the height of the water will be 3 feet.

The correct answer is B.
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by [email protected] » Mon Nov 02, 2015 10:13 am
Hi All,

This question appears in the Diagnostic Quiz at the beginning of the OG13, GMAT2015 and GMAT2016 books. As a side note, there's a typo in the OG13 version though - it states that the water reaches a height of 2 feet (while the explanation states that the height of the water reaches 4 feet). The GMAT2015 and GMAT2016 versions fix this typo.

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