There were 4 guys who wanted to cross the bridge. They were all on the same side of the bridge and it was night, so they needed a light to pass it. Bridge could carry 2 people at once and they had only 1 lamp (light), which even had limited duration of 18 minutes. Those guys need some time to pass the bridge, depends on their condition: A(10 minutes), B(5 minutes), C(2 minutes), D(1 minute).
When 2 guys crossin the bridge, they adopt to the slowest1 (if 1 and 10 goes together, they need 10 minutes).
So it is obvious that 2 guys pass the bridge and one of them (i guess the fastest) must carry lamp back on the other side.
So in what order do they have to pass the bridge, that all come across in 18 minutes or less?
ty
( sry @ tom XDDDD )