Quote:
Originally Posted by Brinty
I first came across that puzzle of Dan's way back in the 60s when I used to subscribe to Scientific American magazine. Martin Gardner had a regular column where he posed some pretty weird puzzles  that was one of them. I spent a whole month trying to figure it out and failed. The only thing I can remember about it now was that it was supposed to be an optical illusion. If you carefully mark it out on graph paper and very carefully cut the pieces out, when you reassemble them the way shown, there is in fact, no hole.
I have to confess that I never tried it but I was prepared to accept Martin Gardner's answer.
Here's another simple one of his . . . .
Step 1. Write down any three digit number.
Step 2. Repeat the digits in the same order to get a six digit number.
Step 3. Divide this six digit number by seven and write the answer down. Don't worry about a remainder  there won't be any.
Step 4. Divide this number by eleven and write the answer down  once again, don't worry about any remainder.
Step 5. Divide this number by thirteen and write the answer down  does this resultant figure look familiar? Does it look like the number you first wrote down?

That's neat Brinty, I did it twice with two different sets of numbers to double check it, LOL