Math, please help I am so confused?

Question

A circular coffee table has a diameter of 5 ft. What will it cost to have the

top refinished if the company charges $3 per square foot for the refinishing?

Answer 1

In a circle Area = 2 * pi * radius.  So the area of the table is 15.7 square feet.  Just multiply 15.7 square feet * $3 per square foot and you get your answer of $47.1

Answer 2

You need to calculate the area of the coffee table top in square feet. Then the cost can be calculated at $3 per square foot.

The area of a circle is given by the formula:

A = pi(r^2)  (say, pi r-squared)

We know the diameter: 5 ft

The diameter is 2 radii, or 2r

so the radius of the circular top is 2.5 ft, or 5/2 ft.

substitute in the formula for the Area, using 3.14 for pi

A = (3.14)(2.5^2) = 19.625 sq ft (approx.)

Multiply 19.625 by $3 = $58.88 (approx.)