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Let right cylinder C have height h and radius r. Let both h and r be >

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Bunuel
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Let right cylinder C have height h and radius r. Let both h and r be > [#permalink] New post   23 Nov 2016, 06:41
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Let right cylinder C have height h and radius r. Let both h and r be >2. If C has equal volume and surface area, what is h expressed in terms of r?

A. h=r
B. h=−r
C. h=1/(r−2)
D. h=rπ/(r−2)
E. h=2r/(r−2)
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E
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Vinayak Shenoy
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Let right cylinder C have height h and radius r. Let both h and r be > [#permalink] New post   Updated on: 15 Dec 2016, 02:53
Bunuel wrote:
Let right cylinder C have height h and radius r. Let both h and r be >2. If C has equal volume and surface area, what is h expressed in terms of r?

A. h=r
B. h=−r
C. h=1/(r−2)
D. h=rπ/(r−2)
E. h=2r/(r−2)



IMO E
volume of a cylinder = pi*r*r*h
surface area= 2*pi*r*r+ 2*pi*r*h
Volume= surface area
pi*r*r*h= 2*pi*r(r+h)
solving we get h= 2r/(r-2)

Originally posted by Vinayak Shenoy on 23 Nov 2016, 07:14.
Last edited by Vinayak Shenoy on 15 Dec 2016, 02:53, edited 1 time in total.
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koenh
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Re: Let right cylinder C have height h and radius r. Let both h and r be > [#permalink] New post   13 Dec 2016, 02:44
Vinayak Shenoy wrote:
2*pi*r*r*h= 2*pi*r(r+h)
solving we get h= 2r/(r-2)


Could you expand on how you solve this last part?
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Re: Let right cylinder C have height h and radius r. Let both h and r be > [#permalink] New post   13 Dec 2016, 04:36
Vinayak Shenoy wrote:
Bunuel wrote:
Let right cylinder C have height h and radius r. Let both h and r be >2. If C has equal volume and surface area, what is h expressed in terms of r?

A. h=r
B. h=−r
C. h=1/(r−2)
D. h=rπ/(r−2)
E. h=2r/(r−2)



IMO E
volume of a cylinder = 2*pi*r*r*h
surface area= 2*pi*r*r+ 2*pi*r*h
Volume= surface area
2*pi*r*r*h= 2*pi*r(r+h)
solving we get h= 2r/(r-2)




Hi,
why is the volume of a cylinder = 2*pi*r*r*h and not just pi*r*r*h ?
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Vinayak Shenoy
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Re: Let right cylinder C have height h and radius r. Let both h and r be > [#permalink] New post   15 Dec 2016, 02:54
germanarmy wrote:
Vinayak Shenoy wrote:
Bunuel wrote:
Let right cylinder C have height h and radius r. Let both h and r be >2. If C has equal volume and surface area, what is h expressed in terms of r?

A. h=r
B. h=−r
C. h=1/(r−2)
D. h=rπ/(r−2)
E. h=2r/(r−2)



IMO E
volume of a cylinder = 2*pi*r*r*h
surface area= 2*pi*r*r+ 2*pi*r*h
Volume= surface area
2*pi*r*r*h= 2*pi*r(r+h)
solving we get h= 2r/(r-2)




Hi,
why is the volume of a cylinder = 2*pi*r*r*h and not just pi*r*r*h ?


Hi Germanarmy, you are right. I made a mistake. its pi*r*r*h. Solving this will give you the answer. I apologize :)
Thanks for correcting :)
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Vinayak Shenoy
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Let right cylinder C have height h and radius r. Let both h and r be > [#permalink] New post   15 Dec 2016, 02:56
koenh wrote:
Vinayak Shenoy wrote:
2*pi*r*r*h= 2*pi*r(r+h)
solving we get h= 2r/(r-2)


Could you expand on how you solve this last part?


I corrected my mistake Koenh. its pi*r*r*h=2*pi*r(r+h)
solving this you get the answer.
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koenh
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Re: Let right cylinder C have height h and radius r. Let both h and r be > [#permalink] New post   15 Dec 2016, 05:12
Vinayak Shenoy wrote:
koenh wrote:
Vinayak Shenoy wrote:
2*pi*r*r*h= 2*pi*r(r+h)
solving we get h= 2r/(r-2)


Could you expand on how you solve this last part?


I corrected my mistake Koenh. its pi*r*r*h=2*pi*r(r+h)
solving this you get the answer.


Thank you for your swift reply!
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Re: Let right cylinder C have height h and radius r. Let both h and r be > [#permalink] New post   13 Aug 2020, 20:28
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Re: Let right cylinder C have height h and radius r. Let both h and r be > [#permalink]
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