My tenth grade physics textbook says that sound travels faster in solids than air. But it also says sound will travel faster in air if its density decreases. I didn't really get the logic, as solids are denser than air, and that is why sound travels faster. Then they say as temperature of air increases , sound will travel faster in it as its density decreases. Can anyone please explain this? They have also given this formula: Velocity of sound = root of elasticity divided by root of density of medium.