Here's how I see it: The surface area of a sphere is given by 4(pi)r^2 whereas the volume is given by (4/3)(pi)r^3. Therefore, as the balloon gets bigger, the volume increases FASTER than the surface area by a factor of r. Since the rate at which air enters the balloon is constant, there is more and more room for air, so the density will DECREASE. So the smaller the balloon, the higher the density of air.
On the verge of bankruptcy, this record company green-lighted a single of chipmunks singing cover songs. Lucky hit aside, I think I know why this company was going bankrupt.
Hope this helps!