Question

A spherical balloon has a circumference of 21 cm. What is the approximate surface area of the balloon to the nearest square centimeter? A. 1,385 cm^2 B. 561 cm^2 C. 346 cm^2 D. 140 cm^2

Answer 1

The answer is D. 140 cm². I think the circumference of the balloon means the circumference of the biggest circle. So the 21=2πr². While the surface area of a sphere is S=4πr². So the S≈140 cm².

Answer 2

Surface area of sphere = 144 cm².

Explanation:

Given : A spherical balloon has a circumference of 21 cm.

To find : What is the approximate surface area of the balloon to the nearest square centimeter,

Solution : We have given that circumference of sphere = 21 cm.

Circumference of sphere = 2 * pi * radius .

Plug the value of circumfrence

2 * pi * radius = 21 cm

2 * 3.14 * radius = 21

radius * 6.28 = 21

On dividing by 6.28 both sides

Radius =
`(21)/(6.28)`

Radius = 3.34 cm

Surface area of sphere = 4 * pi * (radius )².

Surface area of sphere = 4 * 3.14 * (3.34 )².

Surface area of sphere = 144.11 cm²

Therefore, Surface area of sphere = 144 cm².