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# A cylinder of wax is 20 inches tall with a radius of 1 inch. If this c

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SVP
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A cylinder of wax is 20 inches tall with a radius of 1 inch. If this c [#permalink]

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30 Apr 2017, 12:00
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88% (00:46) correct 12% (00:53) wrong based on 34 sessions

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A cylinder of wax is 20 inches tall with a radius of 1 inch. If this cylinder is melted and poured into a new cylindrical mold with a radius of 2 inches, what will be the height of the new cylinder in inches?

A. 5
B. 10
C. 15
D.20
E. 40

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Joined: 28 May 2014
Posts: 528
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Re: A cylinder of wax is 20 inches tall with a radius of 1 inch. If this c [#permalink]

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30 Apr 2017, 22:18
Volume of old and new wax cylinder will be same.
Suppose, height of new cylinder = h;

so,
π*(1)^2*20 = π*(2)^2*h
=>4h = 20
=>h = 5

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A cylinder of wax is 20 inches tall with a radius of 1 inch. If this c [#permalink]

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30 Apr 2017, 22:31
A cylinder of wax is 20 inches tall with a radius of 1 inch. If this cylinder is melted and poured into a new cylindrical mold with a radius of 2 inches, what will be the height of the new cylinder in inches?

A. 5
B. 10
C. 15
D.20
E. 40

Volume of wax in a cylindrical candle is πr$$^2$$h, so if we find volume of wax in the candle to be melted, we can find height of candle with a different radius.

First candle's wax volume is π*1$$^2$$*20 = 20π

Second candle has radius 2, and its volume of wax is also 20π.

For second candle, solve for height: 20π = π*2$$^2$$*h ==> 20π = 4π*h

$$\frac{20π}{4π}$$ = 5 = h. Height of new cylindrical candle is 5. Answer A.
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Re: A cylinder of wax is 20 inches tall with a radius of 1 inch. If this c [#permalink]

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30 Apr 2017, 23:16
Volume of cylinder : pi*r*r*h
Given information: h=20, r=1
New cylinder : pi*2r*2r*h

We know that volume of both cylinders must be common

Therefore, height of new cyclinder must be 4 times smaller. Since the old cylinder has height(20inch), the new cylinder will have height(5inch) (Option A)

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Re: A cylinder of wax is 20 inches tall with a radius of 1 inch. If this c   [#permalink] 30 Apr 2017, 23:16
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