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Lift Puzzle

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    Lift Puzzle

    An hotel has 3 lifts , each one carries a maximum of 30 people. The Hotel has 15 floors and each floor has 5 double bedrooms.

    If it takes 10 seconds for a lift to go up or down one floor , what is the minimum time it takes to empty the hotel in the morning if everyone arrives at the lifts at the same time and the hotel is full.

    (Answer in next weeks magazine)

    I hate it when they do that
    Last edited by Bitbucket; 27 June 2006, 08:51.

    #2
    Originally posted by Bitbucket
    An hotel has 3 lifts , each one carries a maximum of 30 people. The Hotel has 15 floors and each floor has 5 double bedrooms.

    If it takes 10 seconds for a lift to go up or down one floor , what is the minimum time it takes to empty the hotel in the morning if everyone arrives at the lifts at the same time and the hotel is full.

    (Answer in next weeks magazine)

    I hate it when they do that
    Assuming the lifts start in the ideal position, 170 seconds. If they all start on the ground floor 340 seconds.
    "Being nice costs nothing and sometimes gets you extra bacon" - Pondlife.

    Comment


      #3
      This doesnt tell you how long a lift takes to load but I rekon 210 seconds travel time + loading.

      How do you get it to 170 Dave?

      BTW maths is not my strong point.
      Last edited by The Lone Gunman; 27 June 2006, 09:07.
      I am not qualified to give the above advice!

      The original point and click interface by
      Smith and Wesson.

      Step back, have a think and adjust my own own attitude from time to time

      Comment


        #4
        I would just level the building.

        Comment


          #5
          You Daleks

          Originally posted by Purple Dalek
          I would just level the building.
          just because you can't walk up the stairs you level the building, typical me me me attitude. I bet you fsckers all vote conservative.
          (Oops........)
          Why not?

          Comment


            #6
            Originally posted by The Lone Gunman
            This doesnt tell you how long a lift takes to load but I rekon 210 seconds travel time + loading.

            How do you get it to 170 Dave?

            BTW maths is not my strong point.
            Maths isn't my stong point either, having writen it out to check my sums I find that I got it wrong by adding the wrong pair of numbers at some point. 210 does appear to be the right answer

            Anyway, here is how I worked it out.

            The ideal start point is for the lifts to start at the 15th, 12th and 9th floors. Each list collects the people from it's starting floor and the two below it before going to the ground floor.

            Lift one takes 150 seconds from the top floor to the ground floor.
            Lift two takes 120 seconds
            Lift three takes 90 secs.

            On arriving at the ground floor lift three then goes back up to the 6th floor and collects the people from the 6th and 5th floors. 120 second round trip.

            Lift 2 goes back up to the 4th floor and returns with the people from the 4th and 3rd floors. Round trip of 80 seconds.

            Lift 3 goes to the 2nd floor and returns with the people from the 2nd and 1st floors. Round trip 40 seconds.

            Total times for lift 1: 150 + 40 = 190
            Total times for lift 2: 120 + 80 = 200
            Total times for lift 3: 90 + 120 = 210

            So the time for the longest trip to complete, and thus to clear the building = 210 seconds.
            "Being nice costs nothing and sometimes gets you extra bacon" - Pondlife.

            Comment


              #7
              Hold on one cotton picking minute.

              You forgot to take into account the fact that one (or more) of the lifts will develop a fault and break down between floors 2 and 3.

              Therefore, the answer depends on how long the engineer takes to arrive.

              Comment


                #8
                I assumed a ground floor as well as the 15.

                As Dave says. Start lifts at 15, 12 and 9.
                Lift 1 picks up 15, 14 and 13 and takes 150 to reach ground (140 if no ground)
                Lift 2 picks up 12, 11 and 10 and takes 150 to reach ground and get back to 3
                Lift 3 picks up 9, 8 and 7 and takes 150 to reach ground and get back to 6.
                Lift 3 picks up 6, 5 and 4 and takes a further 60 to reach ground again.
                Lift 2 picks up 3, 2 and 1 and takes 30 to ground again.
                Longest round trip is lift 3 which is 150 + 60 which gives 210.
                It works out at 180 if you have no ground floor I think.
                I am not qualified to give the above advice!

                The original point and click interface by
                Smith and Wesson.

                Step back, have a think and adjust my own own attitude from time to time

                Comment


                  #9
                  I made it 240 , but I assumed that lift 3 would pick up passengers from floors 1,2 and 3 as the lift would stop on their floor first so 2 would go to 4,5, and 6.

                  Will have to wait for the answer.

                  Comment


                    #10
                    The original question was what is the quickest possible. You are constraining your own answer.

                    If people at 3,2 and 1 wait before pushing call etc.......
                    I am not qualified to give the above advice!

                    The original point and click interface by
                    Smith and Wesson.

                    Step back, have a think and adjust my own own attitude from time to time

                    Comment

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