Ruby red paint costs $0.50 per square inch. A ball is painted ruby red and costs $100.00 to paint. What is the diameter of the ball?

1 Answer
Jun 9, 2017

8 inch

Explanation:

Space area of ball = 4 pi r^2, where r= radius of ball/sphere

Area of ball * cost of paint per square = total cost of paint,
therefore,
4 pi r^2 * 0.5 = 100

2 pi r^2 = 100

r^2 = 100 / (2 pi)

r = sqrt(100 / (2 pi)) = 10/(sqrt(2 pi)

r = 3.9886 =4 inch

therefore, diameter = 2 * r = 2 * 4 = 8 inch