Four people need to cross a bridge at night. They have one flashlight for the four of them, but the bridge is only wide enough for two to cross at a time. Because it's so dark, anyone crissing the bridge must do so with the flashlight.
Person A can walk across in 1 minute. Person B takes 2 minutes; person C -- 5 minutes, and finally person D needs a full 10 minutes to cross.
Naturally, if two people are crossing the bridge, they move with the speed of the slower person.
What is the shortest amount of time it will take for all four to get to the other side?
The shortest amount of time it will take for the four people to get to the other side is 17 minutes.
The procedure is furnished hereunder as follows:
(i) A and B cross the bridge : 2 minutes
(ii) A comes back with the flashlight : 1 minute
(iii) C and D cross together : 10 minutes
(iv) B takes the flashlight and comes back : 2 minutes
(v) A and B cross together to the other side : 2 minutes
Then, the total elapsed time = (2+1+10+2+2) = 17 minutes
Puzzle Solution
