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kevincan
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sripad
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lanuk
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ell that one is elegant! 8-)
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diegmat
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Kevincan your questions are too tough. :evil:
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muddypaws
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I get B as per working below

sac =surface area of cube
say=surface area of cylinder

for side a,
sac= 6a^2

for raidus r, given height h=2r,
say=2(pi)r(r+h) =2(pi)r(r+2r) = 2(pi)r(3r) = 6(pi)r^2

sac = say ,
6a^2 = 6(pi)r^2
a^2 = (pi)r^2


vc = volume of cube
vy = volume of cylinder

vc = a^3 = a^2*a = (pi)r^2 * sqrt( (pi)r^2 )= (pi)r^3* sqrt(pi)

vy = (pi)r^2*h = (pi)r^2*2r = 2(pi)r^3

vy / vc = 2(pi)r^3 / (pi)r^3* sqrt(pi)
= 2 / sqrt(pi) = 2 / 1.75 = 200/ 175 = 8/7 = appx 1.14

we need (vy / vc ) - 1 = appx 0.14 ie 14%

hence, B ( the minor difference is introduced due to appx sqrt(pi) )

kevincan, for sure
muddypaws tried :-)
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Let SC, VC and s, be the surface area ,volume and length of each edge of cube, and Sc ,Vc and r be the sufrace area , volume and radius of right cylinder.

SC=Sc => 6s^2 = 2pi* r*2r+ 2*pi*r^2=6*pi*r^2

Thus r= s/sqrt(pi)

VC=s^3 Vc= pi*(s/sqrt(pi))^2*2*(s/sqrt(pi)) = 2/sqrt(pi)*VC

So % increase is 100*(2/sqrt(pi)-1)

as 17^2=289 and 18^2=324 , sqrt(pi) is a little more than 1.75=7/4

% increase is a little less than 100/7 and a little more than 100/9



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