Help to Cross Bridge

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A bridge is about to collapse. There are four people P, Q, R and S on one of the sides. Before the bridge collapses, they want to cross it. Now since the bridge is too weak, it can only stand the weight of two people at a time. Also, it is night time and nothing is visible. They have just one torch with them.

Now P takes one minute to cross the bridge, Q takes two minutes to cross, R takes five minutes to cross and S takes ten minutes to cross.

The bridge will collapse in seventeen minutes. How will they be able to cross the bridge before it collapses?

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  • 1 Answer(s)

    Another repeat puzzle. Repeat of the ‘house on fire‘ puzzle.

    1. P and Q cross together first – 2 min. (Even though P can cross in 1 min, he has to slow down because Q is slower than him AND both require the torch.)
    2. P returns with the torch in 1 min. (because he’s alone and hence can move at his maximum speed)
    3. R & S go together – 10 min.  (at the speed of S, the slower of the two)
    4.  Q who is at the other end takes the torch and returns – 2 Min.
    5. Both P and Q cross again – 2 Min.

    Total Time: 2 + 1 + 10 + 2 + 2 = 17 Min.  The bridge collapses, but all have crossed safely.

    Viji_Pinarayi Expert Answered on 20th October 2022.
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