Originally Posted by

**selin** Ok so we could call the mass anything. Because we just want to know if the density will increase or decrease.

Density is p = m / v

We find out the volume of a sphere (balloon) with:

V = 4 * pi * r 3/3

Then you can put this in p = m / v

And get p = m/(4 * pi * r^3) / 3 ---> 3m/(4 * pi * r^3)

Now we can investigate whether the density will increase or decrease. Because the mass does not matter, we can call it for 1.

P = 3 * 1 / (4 * pi * 15 ^ 3) = 7952 g / cm^3

P = 3 * 1 / (4 * pi * 14 ^ 3) = 6465 g / cm^^ 3