# 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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