Posted by **jennifer** on Wednesday, April 18, 2012 at 8:48pm.

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

- algebra -
**Reiny**, Wednesday, April 18, 2012 at 9:47pm
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

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