Alex, Bryan, Jagdish and Julian have to walk through a long dark tunnel. They only have one torch between them so a maximum of two people can go through the tunnel at any one time. Each person takes a different amount of time to get through the tunnel and if two people walk together they must walk at the rate of the slowest.
Alex takes 2 minutes,
Bryan takes 5 minutes,
Jagdish takes 9 minutes,
Julian takes 12 minutes.
What is the least amount of time for all four to walk through the tunnel?
If Jagdish and Julian walk through the tunnel together it will take 12 minutes, If Jagdish then walks the torch back through the tunnel a total of 21 minutes will have passed. Continue till all four are at the other end of the tunnel.
Topics: Starter | Logic | Problem Solving | Puzzles
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Teacher, do your students have access to computers such as tablets, iPads or Laptops? This page was really designed for projection on a whiteboard but if you really want the students to have access to it here is a concise URL for a version of this page without the comments:
However it would be better to assign one of the student interactive activities below.
Here is the URL which will take them to Tran Tunnels, a mathematical adventure.