Find the rate of change of the volume of a ball with respect to its radius r. How fast is the volume changing with respect to the radius when the radius is 2 m?
(2)2 = 16 
m3/m.The cost function C(x), in rupees, of producing x items (x ≥ 15) in a certain factory is given by 
Determine the marginal cost function and the marginal cost of producing 100 items.
Here, 
Marginal cost function 
When x = 100, marginal cost = 20 (100) - 
Find the rate of change of the area of a circle with respect to its radius r when
(a) r = 3 cm (b) r = 4 cm
(a) When r = 3, rate of change of area = 2
× 3 = 6 cm2/cm.
(b) When r = 4, rate of change of area = 2 
× 4 = 8 
cm2/cm.
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