This superb puzzle / brain teaser can be constructed using a sheet of 
paper and scissors.
I recommend a sheet of plain white A4 photocopier paper to start with. 
If you have A5 plain white paper or card it's a better size but do 
start with the A4 otherwise. DO NOT use a 6x4 index card or similar 
until you know 'the trick' - you'll understand why in due course.

        http://www.ultralifebatteries.com/newsletter/ultra_brain_power62.html

I strongly recommend  that you try and work out how it's done before 
you look at the answer.

It's not well explained / drawn.
The paper sheet appears exactly as shown.
The pivoting flap pivots along a line halfway between the two long 
sides so that the top slot forms one edge of the pivot and the bottom 
slot forms the other. The flap can be folded flat to the left when its 
nearest edge aligns with the nearest edge of the left hand slot, or 
folded flat to the right when its far edge aligns with the far edge of 
the right hand slot. Visually its quite amazing on first sight. It's 
obvious how it works "once you know how".

I saw this done in sheet Aluminium many years ago. I don't recall 
whether I worked out how it was done at the time.



        Russell

 

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