June 1, 2010

Problem of the Week

for Tuesday, June 1, 2010

The Bridge of Doom spans a treacherous ravine and has no handrail. You and your three friends must cross this bridge at midnight. Needless to say, you will need to carry a lantern lest you fall to your certain death. The bridge is 100 meters long. You and your friends move at top speeds of 1, 2, 5, and 10 meters per second. No one wants to make a move without the lantern, and the bridge is so narrow that only two people can use the lantern at a time. What plan can you devise to get all four of you across in the least time, and how long does it take?