As a opener at the Science Olympiad Club, we got a bunch of brain teasers to warm up. A bunch of standard ones, you know about the farmer crossing the river with the fox and rabbit and carrots and whatever, that kind of thing. Simple stuff. But there was one problem that threw us.
"Turn this roman numeral into 6 using only one line."
We decided that using roman or arabic numerals wouldn't work, so we tried other options. First: Greek numbers. Failure. Then came our epiphany: maybe we had to write it in binary! 9 in binary is 1001, so maybe if we subtracted a 3 (11 in binary) we'd get 990 in decimal form, which in roman numerals is XM, so maybe if we flipped the whole thing upside down so it looked like XI then turned the I into an M....
We went on like this for a while. I came up with the glorious solution that 6 was 110 in binary. So if we let "X" represent 0, then all we had to do was add another line at the beginning. I was so proud for having figured it out.
I was wrong.
At this point, we'd worked on it for about ten minutes, trying every combination of binary and decimal and roman numerals we could find. Nothing yielded. The teacher hinted that the answer was painfully obvious. And it hit me like a brick wall, disregarding the fact that brick walls are inanimate and incapable of motion, let alone hitting someone. If I really wanted to be in contact with a brick wall, it's I who would have to do the hitting. Just sayin'
So the answer hit me (the answer is also inanimate. See above). I knew it. I danced around the room mocking those poor fools attempting to use Braille. Just kidding. I politely mentioned that I knew the answer.
Are you ready? I'll give you time to shield your eyes by presenting you with this picture of Matthew Lewis/Neville Longbottom
Ok. Are you ready now?
You'd better be.