Here’s a nice, neat puzzle for those with a spare minute.
I was at a mate’s house and saw that he had a desk calendar that worked as follows. The day of the month was displayed using two cubes, which had one number on each face. A quick calculation would suggest that the first cube (the tens column) needs the numbers 0,1,2,3. But the second cube (the ones column) needs the ten numbers 0-9. Each cube only has six faces, so it looks like we’re 4 + 10 – 12 = 2 faces short. So how does it work?
Letters to Nature 