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# Surface Area Word Problems Study Guide (page 3)

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Updated on Oct 3, 2011

### Spheres

A sphere is a round three-dimensional figure in the shape of a ball. An example of a sphere is shown in the following figure.

Think about having to wrap a baseball in paper. The amount of paper needed would be approximately equal to four times the area of a circle with the same radius. Therefore, the formula for the surface area of a sphere is SA = 4πr2, where r is the length of the radius of the sphere.

#### Example

What is the surface area of a sphere with a radius of 3 m? (Leave your answer in terms of π.)

Read and understand the question. This question is looking for the surface area of a sphere when the radius of the sphere is known.

Make a plan. Use the formula SA =4πr2, and substitute r = 3.

Carry out the plan. The formula becomes SA = 4π(3)2. Evaluate the exponent to get SA = 4π(9). Multiply to get the total surface area: SA = 36π m2.

Check your answer. To check this solution, work backward, and divide the total surface area by 4π: 36π divided by 4π is equal to 9. Take the positive square root of 9 to get r = 3. This answer is checking.

Find practice problems and solutions for these concepts at Surface Area Word Problems Practice Questions.

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