Hard word problem

Question

THe weight of a synthetic ball varies directly with the cube of its radius. A ball with a radius of 2 inches weights 0.80 pounds. Find the weight of a ball of the same material with a 3 inch radius.

Answer 1

The cube of the first radius is

 

2³  = 8

 

The cube of the second radius is

 

3³ = 27

 

Set up a propotion to solve for the missing weight

 

8/27 = .8/x

 

Cross muliply

 

8x = 21.6

 

x = 2.7