Crossing the Bridge Puzzle (Bridge and torch problem)

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?

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Anand Guru Asked on 13th July 2015 in Amazon Interview Puzzles.
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  • 2 Answer(s)
    Best answer

    Solution to the problem is as follows:

    Move Time
    A & B Cross with torch 2
    A Return with torch 1
    C & D Cross with torch 10
    B Return with torch 2
    A & B Cross with torch 2
    ———————— ————–
    Total Time 17
    Anand Guru Answered on 13th July 2015.
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    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!

    Detective Expert Answered on 13th July 2015.
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