Wednesday, June 2, 2010
The family is composed of a father, mother, grandfather, and child. The father is athletic and can cross the bridge in 1 minute; the mother can cross in 2 minutes; the child can cross in 5 minutes; and the grandfather, the slowest, takes 10 minutes to cross. They have a lantern with them.
Since it's pitch dark, the bridge can't be crossed without the lantern. The bridge is so narrow that only two can cross at a time, and each pair can only move as quickly as its slowest member.
Their pursuer is likely not far behind. What is the quickest way to get everyone across the bridge?
They can all get across in 17 minutes. Thanks to Rob Strong for articulating the solution.
F&M cross: 2 min
F returns: 1 min
GF&C cross: 10 min
M returns: 2 min
F&M cross again: 2 min.
Posted by Charlie Guthrie at 12:00 AM