Calculus related rates:
if a snowball melts so that its surface area decreases at a rate of 7 cm2/min, find the rate at which the diameter decreases when the diameter is 10 cm.

The snowball is a spherical figure and the surface area of the ball is calculated through the equation,
                        S = πD²
where S is surface area and r is the radius. Differentiating the equation gives,
                          dS/dt = 2πD(dD/dt)
Substituting the given,
                              7 = 2π(10)(dD/dt)
The value of dD/dt from the given equation is 0.11 cm/min.

The answer would be choice b