Posted by ankur on .
a spherical ballon is being inflated at the rate of 10 cu in/sec.find the rate of change of area when ballon has a radius of 6 inch.
(a)3.33 in2/sec
(b)3.67 in2/sec
(c)3.11 in2/sec
(d)none of these

maths 
Reiny,
V = (4/3)πr^3
dV/dt = 4πr^2 dr/dt
when r = 6 , and dV/dt = 10
10 = 4π(36) dr/dt
dr/dt = 10/(144π) = 5/(72π)
A = 4πr^2
dA/dt = 8πr dr/dt
when r = 6
dA/dt = 8π(6)(5/(72π) )
= 30/9 = 10/3
= appr 3.33 > looks like a)