Help me! (1 Viewer)

[jaycoo]

Ok so I was looking through my ext maths exam and there is a question I got wrong. I don't know what I did wrong or how I even figured out the answer.

The question is:

What is the volume of a sphere with a radius double that of a sphere with a volume of 29mm3?
(btw the 3 is supposed to be a cubed)

My answer was 229.8mm3 but the correct answer is 232mm3.

How would you work out the answer to this question?

Thanking you in advanced!

 

[HSC2014]

In the formula 4/3 (pi) r^3: Focus on r^3 (since this is what is changing)

If we double the radius, it is now (2r)^3 = 8r^3

Therefore we can see it increases by a factor of 8.

29x 8 = 232