Madison, Abigail, Olivia and Isabella 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.
Madison takes 2 minutes, Abigail takes 3 minutes, Olivia takes 5 minutes, Isabella takes 8 minutes. What is the least amount of time for all four to walk through the tunnel? 
Notes: 
Example:
If Olivia and Isabella walk through the tunnel together it will take 8
minutes, If Olivia then walks the torch back through the tunnel a total of 13 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
19 minutes:
Madison and Abigail walk through taking 3 minutes
Madison walks back with the torch taking 2 minutes [5 minutes total]
Olivia and Isabella walk through taking 8 minutes [13 minutes total]
Abigail walks back with the torch taking 3 minutes [16 minutes total]
Madison and Abigail walk through taking 3 minutes [19 minutes total]
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