Posted by Jordan on Monday, January 9, 2012 at 3:50pm.
A spherical ballon is leaking air at 2 cubic inches per hour.l How fast is the ballons radisu chancing when the radisu si 3 inches.

math (Caluclas)  Steve, Monday, January 9, 2012 at 4:00pm
v = 4/3 pi r^3
dv/dt = 4pi r^2 dr/dt
2 = 4pi*9 dr/dt
dr/dt = 2/36pi = 1/18pi = .0177 in/hr 
Caluclas ?  Reiny, Monday, January 9, 2012 at 4:01pm
What is a radisu?
Once I can understand as a typo, but twice ?
V= (4/3)πr^3
dV/dt = 4π r^2 dr/dt
2 = 4π(9)dr/dt
etc. 
math (Caluclas)  Jordan, Monday, January 9, 2012 at 4:06pm
Sorry about that Reiny. I have a quick question though, where does the 9 come from?

math (Caluclas)  Reiny, Monday, January 9, 2012 at 4:17pm
Notice both Steve and I have the same derivative equation of
dV/dt = 4π r^2 dr/dt
what is the value of r^2 when r = 3 ? 
math (Caluclas)  Jordan, Monday, January 9, 2012 at 4:24pm
Oh okay. I understand that, i was just not understand where the 9 came from, but i see now. Thank you both