I duno whether anyone know this. Anyway, here it goes:
There is a long bridge.
10 minutes journey from one end to the other end.
And situated on the middle of the bridge is a security stand.
Inside the stand, there is the security guard.
He prevents anyone from crossing from one end to the other
end.
He rests for 5 minutes after 20 minutes of work.
After resting, he continues to work, so on and so forth.
However, a little boy managed to cross the bridge
sucessfully.
How? 
