A gun shots bullets with different speed each second.
The bullets form a straight line.
The bullets keep their speed (not getting slower or faster).
But if 2 of the bullets collide, 2 of them are destroyed (annihilated)
The gun stops after 12 bullets fired.

What is the probability that all the bullets will be destroyed ?

There is a beautiful math formula for every even bullets fired, find it!

This is a puzzle from a good website, I will show the link after the puzzle solved.