sound velocity

So it says in TBR that speed of sound in gas is square root (constant * pressure/ density).

I don't understand why speed would decrease with increase in density. I thought if density was higher, then the molecules would be closer together then collision and transfer of energy to occur faster? This would allow the sound wave to travel faster.

It says later in the book that the speed of sound is square root( restoring force/ molecular inertia). How is molecular inertia related to density?...

sound velocity