Lots of similar puzzles exist on internet – with different stories on different places with different people different time but the principle stays the same.
Group of friends is trapped in a burning house. The house is going to collapse in 12 minutes so they desperately want to get out. They have to run through a hallway which is in flames. If someone wants to pass through he has to have a fire extinguisher to hold the flames back at least a little. Problem is that the friends have only one.
Only two people can go at once. Than somebody has to return with the extinguisher and other two can go.
There is one fireman among the friends who moves through flames with ease and he can ran through the hallway in one minute. His best friend who is in great shape can run through in 2 minutes. There is an older man who needs four minutes and a drunken guy who will need 5 minutes to pass through. If two people go together they move at speed of the slower one.
How will they do it so that they all get out before the house collapses?
It is really possible. Not only the one who just came out can go back.
Fireman and friend out.......2 min.
Fireman back.................1 min
Drunk and old one out....5 min
Good-shaped friend back..........2 min
Fireman and friend out....2min
Two best friends are running out of the door and the house goes off...:)