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right cylinder

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right cylinder

by ska7945 » Tue Sep 02, 2008 8:40 pm
A certain right circular cylinder has a radius of 5 inches. There is a kind of liquid filled in this cylinder to the height of 9 inches. If this liquid is poured completely into a second right cylinder, then the liquid will fill the second cylinder to the height of 4 inches. What is the radius of the second cylinder, in inches?

A. 6
B. 6.5
C. 7
D. 7.5
E. 8

oa D
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by mayur00 » Tue Sep 02, 2008 8:54 pm
Eq. 1

volume of liquid = pi*5^2*9 = 25 * 9 * pi

Let the radius of the second cylinder be 'r'

then pi * r^2 * 4 = 25 * 9 * pi

therefore, r = sqrt (25 * 9 / 4) = 7.5

The reason I didn't multiply 9 and 25 is because both are perfect squares which makes the calculation easier.
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