Riley, Haley, Gabrielle and Nicole 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.
Riley takes 3 minutes, Haley takes 5 minutes, Gabrielle takes 8 minutes, Nicole takes 10 minutes. What is the least amount of time for all four to walk through the tunnel? 
Notes: 
Example:
If Gabrielle and Nicole walk through the tunnel together it will take 10
minutes, If Gabrielle then walks the torch back through the tunnel a total of 18 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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Previous Day  This starter is for 8 February  Next Day
28 minutes:
Riley and Haley walk through taking 5 minutes
Riley walks back with the torch taking 3 minutes [8 minutes total]
Gabrielle and Nicole walk through taking 10 minutes [18 minutes total]
Haley walks back with the torch taking 5 minutes [23 minutes total]
Riley and Haley walk through taking 5 minutes [28 minutes total]
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