Riddle Keeper

Four people need to cross a rope bridge at night. The bridge is very old and some boards are missing. Luckily the group brought along a flashlight. Unluckily the bridge can only support the weight of two people at a time and it’s too far to throw the flashlight back across the bridge once someone has crossed, which means someone will need to bring it back to the remaining members of the party.

Things get interesting when you find that our party members take different lengths of time to cross the bridge. The first takes one minute, the second takes two, the third takes five and the fourth takes ten minutes. When two people cross the bridge they travel at the speed of the slower person (so if the one and ten minute members walked across together, they would take ten minutes).

Your job is to figure out the fastest way to get them across the bridge. Your first answer, nineteen minutes, is too long.

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