Puzzles & Quizzes

Can You Solve the Toggler Brain Teaser?

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Plenty of brain teasers deal with truth and lies, but how many do you know that toggle between them? Get ready to solve this head-scratcher of a logic puzzle.

Here's the Puzzle

There are five people in front of you: one truth-teller and four togglers. A truth-teller will always tell the truth (obviously). A toggler will answer a question with either a lie or the truth, but if you ask the same toggler another question, they will do the opposite of what they did the first time.

For example, say a toggler's name is Zach, he's from California, and he loves video games. You ask him his name and he says, "Penelope." That's a lie, so the next question you ask him — say, where he's from — he'll tell the truth and say "California." Then the next question you ask him will be a lie. You might ask if he loves video games, and he'd say no. The opposite is also true, so if his first answer is the truth, his second answer would be a lie and his third answer would be the truth. You don't know whether they'll lie or tell the truth for the first question, and you also don't know which people in front of you are togglers or truth-tellers.

Here's the question: How can you find the truth-teller by only asking two questions? The questions could be to two different people or both to one person, and you can choose the second question after getting your answer for the first. Give it a try, then watch the video below or scroll down for the answer.

The Toggler Brain Teaser

Key Facts In This Video

  1. This is the toggler brain teaser: 00:57

  2. This is the solution to the toggler brain teaser: 05:54

Here's the Answer

Ready for the answer? You should ask both questions to the same person. Your first question should be "Are you the truth-teller?" If the answer you get is "Yes," you know you either have a truth-teller or a lying toggler. In that case, you know the toggler will tell the truth next (and you know the truth-teller will always tell the truth) so you can just ask the question you need the answer to: "Who is the truth-teller?" Whoever you're asking, they'll truthfully point to the truth-teller.

If, on the other hand, the answer you get is "no," you know you have an honest toggler. There's no other option since a truth-teller would always say "yes." That means the next answer you get will be a lie, so you simply make the question you asked in the first scenario negative: "Who is not the truth-teller?" That toggler will lie and point to the truth-teller, and you'll have your answer.

Did you get the answer? Watch the video above for more help solving the puzzle.

Written by Curiosity Staff November 10, 2015

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