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 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?

Solution

Information provided:

Time in which bridge will collapse = 17 mins

Number of people wants to cross the bridge = 4 people

Number of torch they have = 1

Time take by A to cross the bridge = 1 minute

Time taken by B to cross the bridge = 2 minutes

Time  taken  by C to cross the bridge = 5 minutes

Time taken by D to cross the bridge = 10 minutes

 

Move                                      Time

A & B Cross with torch                    2 min

A return with torch                       1 min

C & D Cross with torch                    10 min

B return with torch                       2 min

A & B cross with torch                    2  min


Total time                                17 min

Detail Analysis

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 & B crosses the bridge in 2 mins and returns with the torch in 1 mins, so total time taken by now is 3 mins.
Time left before the bridge collapse = 14 mins
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?
C & D crosses the bridge in 10 mins and B returns with the torch in 2 mins, so total time taken by now is 15 mins.
Time left before the bridge collapse = 2 mins
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?
Now, A & B were only left out and and time left before the bridge collapse is 2 min but the maximum time taken by A & B to cross the bridge is 2 mins as time taken by A is 1 min and by B is 2 mins.
Hence A, B, C ,and D all four will cross the bridge within 17 mins.