>>21
Try doing this once. Multiply 43×76×52 without doing two at once taking this result and multiplying it by the other digit. Now ask someone who is 13 1/2 years old. I was able to do just that! I've explained the trick so well that almost anyone should be able to understand it. This is that trick explained very clearly (opens a new window). I wondered, if you can add a group of numbers like 43+76+52, can you multiply a group of numbers. During my first year at Triangle YMCA camp, I did just that. I figured out the secret behind it while in the lower floor of the dining place near the swimming pond.
As the story goes, the place is rather empty. There are a few others in here, but not many. I'm near the bathrooms on what appears to be a ground freezer (a freezer that covers more ground space rather than standing upright and otherwise lacks shelves). This freezer is white. I've got a piece of paper and I'm doing some math questions on it. I then put a column of 11's and tried to multiply them. I got 12221 as my first result. When I did the x-0-1 combo, I had two zeros rather than 1 and the x-1-1 had three zeros rather than two and thus the cause to this. I multiplied two elevens together and got 121. I then took that result and multiplied by 11 and got 1331. I then had to find a way to get 1331 and it just so happened to be that I had too many zeros on the end. I repeated for a triplet of 22's. When I tried a triplet of 33's, which had carrying involved, that went okay, but I can vaguely recall this. It was when I tried a triplet of 99's that I came across a problem with carrying. 9×9×9 is 729. I wrote the 9 down, but didn't know what to do with the 7 and the 2. I soon figured out that the remains should be carried over in full (adding 72 on the end rather than 7, 2, or 9). From there, I tried some randomized numbers and it worked out every time. I never knew why it worked out, but it just did and that's all I cared for at the time. It was a great discovery and considering that even some college students wouldn't otherwise know the trick, someone who just finished elementary school figured out the trick!