Solutions to WU’s puzzles and riddles : Bridge Crossing (medium)

Bridge Crossing

I am trying to find all the solutions and put them together at a single place, So feel free to add comments and if you have a solution please do post. Cheers … 🙂

Here is the puzzles link : http://www.wuriddles.com/

Question :

Four people, A, B, C, and D, are on one side of a bridge, and they all want to cross the bridge. However, it’s late at night, so you can’t cross without a flashlight. They only have one flashlight. Also, the bridge is only strong enough to support the weight of two people at once. The four people all walk at different speeds: A takes 1 minute to cross the bridge, B takes 2 minutes, C takes 5 minutes, and D takes 10 minutes. When two people cross together, sharing the flashlight, they walk at the slower person’s rate. How quickly can the four cross the bridge?

Note: Supposedly a classic Microsoft question.


1 Response to “Solutions to WU’s puzzles and riddles : Bridge Crossing (medium)”

  1. 1 groliks
    July 24, 2016 at 6:32 pm

    17 minutes.

    First crossing: A+B = 2 minutes (B stays on the other side)
    First return: A = 1 minute
    Second crossing: C+D = 10 minutes (A waits at starting point)
    Second return: B = 2 minutes
    Third crossing: A+B = 2 minutes

    Total time: 17 minutes.

    The key is to minimize the time taken by two slowest persons, by combining the two.

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