The Romans used weird, weird math. To multiply two terms, they repeatedly doubled one of them in one column while halving the other term in another column, throwing away any remainders that came up, crossed off half the numbers in the first column, added up what remained, and — voila! — got the right answer.
How on earth did they come up with it? And why on earth does it work?
Here’s what it looks like. If you’re not a mathy person, don’t worry, I’m not asking you to do any calculations–just to enjoy the strangeness.
1. Start with two numbers
536 * 42
= (500 + 30 + 5 + 1) * (40 + 2)
= DXXXVI * XXXXII
2. Multiply the first column and halve the second
|Multiply these||Divide these|
3. If a number in the second column is even, cross it off in the first column.
4. Add up all the remaining numbers in the first column.
= 22,000 + 500 + 10 + 2
5. And here’s the answer!
That’s all I have. If you want to know why it works, one of these links should satisfy.
Or, if this is too much math for you, just be glad I didn’t tell you about multiplying infinity.