Crossing the Bridge Puzzle

March 21, 2023

Crossing the Bridge

In 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 minutes and “D” takes 10 minutes. How do they all cross before the bridge cross ?

Solution

Here we have provided information for the solution of Crossing the Bridge Puzzle :

Time in which bridge will collapse = 17 mins

Number of people who wants to cross the bridge = 4 people

Number of the torch they have = 1

Time taken by A to cross the bridge = 1 minute

Time is taken by B to cross the bridge = 2 minutes

Time is taken by C to cross the bridge = 5 minutes

Time is 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 & B crosses the bridge in 2 mins and returns with the torch in 1 min, so the total time taken by now is 3 min.

Time left before the bridge collapsed = 14 mins

C & D crosses the bridge in 10 mins and B returns with the torch in 2 mins, so the total time taken by now is 15 min.

Time left before the bridge collapsed = 2 mins

Now, A & B were only left out and the time left before the bridge collapsed in 2 min but the maximum time taken by A & B to cross the bridge is 2 mins as the time taken by A is 1 min and by B is 2 mins.

Hence A, B, C, and D four will cross the bridge within 17 mins.