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Crowded corridor brainteaser

By , 24 June 2020

Difficulty: Fun
The extension is finished! Five new classrooms have been added to the main building. But there’s a problem.
The corridor to the new classrooms is very busy. When the bell goes, lots of students stream out of the extension, while others rush in. It gets really crowded!
To solve the problem, Mr Wigg put up a sign:

“Students entering the extension please stay left!
Students leaving the extension please stay right!”

But Mr Wigg’s sign only made the problem worse. Can you see why?

Scroll down or click for a hint, or the answer!

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Brainteaser hint

Try it out for yourself! Walk one way down a corridor with your left hand on the wall. Then walk the other way down the corridor with your right hand against the wall!

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Brainteaser answer

Mr Wigg’s sign will cause lots of collisions!
The left hand side when you’re entering the extension is the same as the right hand side when you’re leaving. So all the students will end up on the same side of the corridor, running into each other.
The correct sign would just say:
“All students please stay left!”
That’s exactly how our roads work!

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  1. This was a problem easy to solve in the school in which I taught. The rule was:
    ‘Keep left!.’

  2. That’s a Brainteaser?

    1. Some brainteasers are easier than others!

      In all seriousness, we’ve surveyed readers of our publications many times, and they tend to say our brainteasers are very hard. So we’re always looking for easier puzzles to add to the mix.


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