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Moderator  Joined: 18 Apr 2015
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30% of the surface area of a right circular cylinder is shad [#permalink]
Expert's post 00:00

Question Stats: 100% (00:41) correct 0% (00:00) wrong based on 2 sessions
30% of the surface area of a right circular cylinder is shaded. If the diameter of the base of the cylinder is 10 and the height is 4, what is the surface area of the unshaded region?

A. $$27\pi$$

B. $$40\pi$$

C. $$63\pi$$

D. $$70\pi$$

E. $$90\pi$$
[Reveal] Spoiler: OA

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Director  Joined: 07 Jan 2018
Posts: 604
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Re: 30% of the surface area of a right circular cylinder is shad [#permalink]
knowing the formulas for volumes and surface area of solid figure is useful
surface area of a cylinder = 2pi*r(r+h)
since diameter $$= 10$$; $$r = 5$$

Find the total surface are of the cylinder $$= 2*pi*5(5+4) = 90pi$$
$$30$$% of $$90pi$$ $$= 27pi$$ which is the shaded area hence
unshaded area $$= 90pi-27pi = 63pi$$
option c
_________________

This is my response to the question and may be incorrect. Feel free to rectify any mistakes

Last edited by amorphous on 24 Apr 2018, 01:42, edited 2 times in total.
Edited by Carcass Moderator  Joined: 18 Apr 2015
Posts: 5919
Followers: 96

Kudos [?]: 1159  , given: 5501

Re: 30% of the surface area of a right circular cylinder is shad [#permalink]
1
KUDOS
Expert's post
if you use $$\pi$$ copying and paste it from the web, then when you wrap it up with $$tag m$$ the result are strange symbols.

Instead, just write simply \pi and wrap with $$tag m$$

the result is this $$\pi$$ _________________ Re: 30% of the surface area of a right circular cylinder is shad   [#permalink] 24 Apr 2018, 01:43
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