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

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