Physics: Why do sound waves travel faster in warm air than in cold air?

I thought sound waves traveled faster in denser substances...?

Cold air is denser.

warm becuase cold air is dense so the sound has to pas through more objects but its marginal

Think about what is happening to air particles at a warm temperature. They are moving much more rapidly on average. So in a small spot there are more likely to be more particles. The more particles the easier it is for a sound wave to move through the air.

in warm air the molecules have more kinetic energy so the molecules moves fastly and propogate sound fastly because the sounds move by the vibration of molecules

Sound waves cannot move faster in warm air. The question is based on the incorrect information. Cool air is dense than the warm air and it offers a good medium for the sound waves to pass through. That is why we can hear the railway whistles from very far during morning time. There are no other noises and air is dense.

The speed of sound c is equal to the square root of the bulk modulus (or bulk "stiffness", the inverse of its compressibility) divided by the density. (See ref. 1) When air warms, its density decreases but the bulk stiffness stays the same unless there's a pressure change, so c increases.
EDIT: The answer that denies the premise of the question is wrong. There is a temperature dependence formula (see ref. 2) that shows a positive speed temperature relationship: c = 331.3 + (0.606 * Temp C).
There's a widespread misconception that more density = greater speed. It's stiffness, not density, that contributes to increased speed. Sound does tend to travel faster in denser materials, because such materials tend to have a higher stiffness/density ratio, but it isn't always true. That's why the speed of sound in hydrogen is nearly as great as that in lead. And the fastest sound velocity known, 12,870 m/s, occurs in one of the less-dense metals, beryllium.