Aballoon has a circumference of 23 cm. use the circumference to approximate the surface area of the balloon to the nearest square centimeter.

To get the surface area of a sphere, we need to have the radius. We are given the circumference. The circumference formula is C=2πr.  We need to solve for r. 
23 = 2πr
r=3.66

The calculation for surface area is A = 4πr^2. 
A = 4π(3.66)^2

Solve for A.

A= 168 cm^2.

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