Can you solve the bridge riddle?

 Can you use math to get you and your friends over the bridge before the zombies arrive?

It is night. Four scientists are escaping from zombies. They have one lantern between them. They reach a gorge, spanned by a log bridge. They need to cross the gorge before the zombies arrive, and then destroy the bridge.

As with all such puzzles, there are various artificial constraints:

– The scientists have 17 minutes before the zombies arrive, so they must cross the gorge in less than 17 minutes.

– Only two people can be on the bridge at the same time or it will not hold them.

– They need the lantern to cross – they can’t cross in the dark (It’s a long bridge and an old-fashioned lantern. You can barely see your feet; you can’t see very far ahead or behind on the bridge). But it’s OK to be left alone in the dark on one side or the other.


It gets more complicated:

– Person A takes 1 minute to cross

– Person B takes 2 minutes to cross

– Person C takes 5 minutes to cross

– Person D takes 10 minutes to cross

Your job is to get everyone across the bridge, never more than two on the bridge at a time, always a lantern on the bridge, in under 17 minutes so they outwit the zombies.

The answer is in a video below.

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