Question

A balloon has a circumference of 22 in. Use the circumference to approximate the surface area of the balloon to the nearest square centimeter.

Answer 1

Surface area of a sphere (balloon) is S=4*pi*r^2. So all you need is the radius of the balloon.

Since circumference of the balloon is given, we can find the radius using: C=2*pi*r:
solving for r, we get

r=C/(2*pi)
= 22/(2*pi)

Now put this value for r into the surface are formula and get your answer... :)