Question 1111440
A large snowball with a radius of 2.1 feet is melting so the radius is decreasing at 0.4 feet per hour.  How fast is the surface area changing when the radius is 0.8 feet?
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SA = 4pi*r^2
dSA/dt = 4pi*2r*dr/dt
dSA/dt = 4pi*2*0.8*0.4 sq ft/hr
= 2.56pi sq ft/hr