The 17 minutes Crossing the Bridge Puzzle

By | November 10, 2016

Crossing the Bridge Puzzle

Crossing the Bridge Puzzle: A bridge will collapse in 17 minutes.

4 people want to cross it before it will collapse. It is a dark night and there is only one torch between them.

Only two people can cross at a time.

“A” takes a minute to cross.
“B” takes 2 minutes.
“C” takes 5
and “D” takes 10 minutes

How do they all cross before the bridge collapses?


A and B cross first using up 2 minutes.
A comes back making it 3
C and D cross making it 13 minutes
then B crosses back over making it 15 minutes.
And finally A and B cross together to make it 17 minutes!


Detailed Solution to the problem is as follows:

Move Trip Time Total Time
A & B Cross with torch 2 2
A Return with torch 1 3
C & D Cross with torch 10 13
B Return with torch 2 15
A & B Cross with torch 2 17
———————— ————– ————–
Total Time 17