Thread: Help! Related rates with the chain rule

Here is the question
I inflate a spherical balloon by blowing 1000cm^3 of air into it every 5 seconds.
a/ what is the rate of change of the volume of the balloon (in cm^3/sec), at the moment when the radius of the balloon is 5cm?
b/ what is the rate of change of the radius of the balloon (in cm/sec), at the moment when the radius of the balloon is 5cm?

So the Dv/Dt is (-200cm^3/sec) right? Then what?
Please Help!!

V =4/3pi^r^3

dV/dt = 4pi*r^2*dr/dt

Now use your data