The Gizmodo Monday Puzzle is back from summer hiatus! After a long season of sunshine, flip flops, and mental atrophy, it’s time to fall back into the cool, brisk world of rationality. Our last challenge before the break was also our most controversial yet. The comments section bubbled with animated debate over the stunningly counterintuitive card puzzle. Shout out to reader Enfy for your crisp explanations of the solution and for helping me stave off a mutiny.
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Tonight marks the eve of All Hallows’ Eve, so to honor the scariest time of the year, we’re stranding you in a ghastly hellscape. Zombies are after your brain, and that’s exactly what you’ll need to use to survive.
One of these is a classic problem dressed in a Halloween costume. The other is a devilish variant.
Puzzle #17: Poisoning Zombies
Zombies have taken over the world, and you preside over a stronghold with a group of humans trying to build a normal life. You have 1,000 barrels of water to hydrate your people, but your chief scientist comes to you one morning with some disturbing news: there’s been a contamination of the water supply, and one of the 1,000 barrels is now poisonous, but he lost track of which one.
The poisoned water looks and tastes like all of the others, but if anyone drinks even a drop, then they will suddenly fall dead that midnight. You don’t want to risk lives, but since Hollywood has universally agreed that zombies have no moral worth, you are willing to capture and poison them to discover the bad barrel.
Snaring zombies is hard work. What is the fewest number of zombies you’ll need to identify the poisoned barrel by tomorrow?
Puzzle #17b
Here’s a bonus puzzle: What is the fewest number of zombies you would need if you had 2,000 barrels and two days to run tests?
Neither problem is easy, but the second is much tougher to conceptualize, and I don’t recommend trying it until you’ve solved the first one. If you’d like a small hint for each, I’ll do you one better and just give you the answers. Because determining the number of zombies you’ll need isn’t really the puzzle, but rather how you’ll use them.
So if it helps, for 1,000 barrels in one day you’ll need this many zombies. For 2,000 barrels in two days, you’ll need this many zombies.
As a reminder, we encourage open discussion and collaboration in the comments, but this means you might encounter unwanted spoilers there. We will post the solution and a new puzzle next Monday. Good luck and happy Halloween.
Do you know a cool puzzle, original or otherwise, that you think should be featured here? Message me on Twitter @JackPMurtagh or email me at [email protected]