algebra
posted by jennifer .
the weight of a symetry ball varies directly with the cube of it's radius a ball with the radius of 2 inches weighs 5.60. find the weight of a ball with a 3 inch radius

weight = k r^3 , where k is a constant
when r = 2, weight = 5.6
5.6 = k(2^3)
k = 5.6/8 = .7
so weight = .7r^3
when r = 3
weight = .7(27) = 18.9
or ... just use a ratio
w/5.6 = 3^3/2^3
w = 5.6(27/8) = 18.9