The mafia has kidnapped you and says that if you answer a question of theirs correctly that they will let you go free:

There are 4 guns on a table in front of you and another is being held to your head. Of the 5, one gun has 1 chamber, one has 2 chambers, one has 3, another 4 and the last has 5 chambers.

The person holding the gun to your head says that he chose it at random amongst the other 4 and put a random amount of bullets in it from 1 to the amount of chambers that were available.

The question you have to answer to avoid risking death is: If he pulls the trigger once, what is the chance that you will be shot and die regarding the information you have been presented with?