The diameter of a sphere is doubled. what is the new volume of the sphere?

Remember, the diameter is . So if the diameter is doubled, then the new radius is  units (instead of "r" units) 

 Start with the given equation. 

 Replace the original "r" with "2r". 

 Square 2r to get  

So the old equation is  and the new one is  

The ratio of the new surface area to the old surface area is then: 

 

 Highlight the common terms 

 Cancel out the common terms 

 Simplify 

So the new surface area is simply 4 times the original surface area. So the answer is B