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?

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Answer 1 · 2017-06-09T05:02:45

#8 # inch

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