Posted by jonh on Sunday, March 10, 2013 at 4:54pm.
let the radius be r
let the height be h
Volume = πr^2h
πr^2h = 400
h = 400/(πr^2)
cost = different prices x surface areas
= .03(2πrh) + 2(.06) πr^2
= .03[2πr(400/πr^2) + 4πr^2]
= .03[ 800/r + 4πr^2]
d(cost)/dr = .03[ -800/r^2 + 8πr] = 0 for a min of cost
800/r^2 = 8πr
100/π = r^3
r = 3.169
h = 400/(π(3.169)^2) = 12.679
check my arithmetic
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