Miquel, Colin, Cody and Alejandro 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.
Miquel takes 3 minutes,
Colin takes 4 minutes,
Cody takes 6 minutes,
Alejandro takes 7 minutes.
What is the least amount of time for all four to walk through the tunnel?
If Cody and Alejandro walk through the tunnel together it will take 7 minutes, If Cody 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.
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Miquel and Colin walk through taking 4 minutes
Miquel walks back with the torch taking 3 minutes [7 minutes total]
Cody and Alejandro walk through taking 7 minutes [14 minutes total]
Colin walks back with the torch taking 4 minutes [18 minutes total]
Miquel and Colin walk through taking 4 minutes [22 minutes total]
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