# math

The area of a spherical balloon expand at a rate of 0.4cm square/s .find the rate at which its volume expand when the radius is 12cm

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1. a = 4πr^2
da/dt = 8πr dr/dt

v = 4/3 πr^3 = ar/3
dv/dt = 1/3 (r da/dt + a dr/dt)
Now just plug in your numbers

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