Gabriella, Jenna, Kimberly and Stephanie 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.
Gabriella takes 2 minutes, Jenna takes 5 minutes, Kimberly takes 9 minutes, Stephanie takes 10 minutes. What is the least amount of time for all four to walk through the tunnel? 
Notes: 
Example:
If Kimberly and Stephanie walk through the tunnel together it will take 10
minutes, If Kimberly then walks the torch back through the tunnel a total of 19 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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