Go forth and do not multiply (not what you think)

But first, for those who never read comments...

In the previous post, I included several answers from Jeopardy! including "What is D?", a response to the clue "The letter after C in the Roman numeral for 400." In a comment, a reader named kylie who lives in Australia said, "My brain has absorbed Roman numerals as well as it has because of watching movies. All of them were made in MCM something so by a process of deduction I could have eventually remembered that C = 100 but I would have been too slow for Jeopardy. I didn't remember D because it didn't appear in movie dates."

I replied to kylie that if all of the movies she has seen were made in MCM something then she hasn't seen a movie in XXIV years, since MCMCXIX, in fact, because movies since then have been made in MM something.

It occurred to me later that perhaps the reason most American brains have absorbed Roman numerals as well as they have is related more to the Statue of Liberty than to movie dates. The very tall woman in New York harbor not only holds aloft a torch with one arm but also cradles in the other arm a tablet engraved with the date JULY IV MDCCLXXVI, the date our Declaration of Independence from England was signed in Philadelphia, Pennsylvanis -- July 4, 1776.

This time last year I was learning to read Hebrew (not the same as understanding Hebrew). This year I have stumbled across a new way to solve multiplication problems without actually multiplying the numbers together. I tried it several tims and it works.

Suppose you want to solve the following multiplication problem:

15 × 12

We are going to make two columns of numbers. We will call the left column L and the right column R (clever, huh?). Put 15 in the top row of column L and put 12 in the top row of column R.

So far, so good.

Let us continue.

In each row of column L, enter half the number above it, discarding any fraction (that is, half of 15 for our purposes will be 7, not 7.5) until the last row of column L contains "1". In each row of column R, enter double the number above it. In our 15 × 12 problem, your 2-columns will look like this:

15				12
7				24
3				48
1				96

We are not yet done. Here are the three most important things you need to know.

1. If every number in column L is an even number (except the last row, of course, which will always contain "1"), then the last row of the other column (column R) contains the correct answer to the problem L1 × R1.

2. If every number in column L is an odd number, add all the numbers in the other column (column R) together (R1 + R2 + R3, etc.) and the resulting sum is the correct answer to the problem L1 × R1.

3. If column L contains both odd and even numbers, identify (by marking through) all rows in R whose corresponding L row contains an even number. Add together the numbers that remain in column R and the resulting sum is the correct answer to the problem L1 × R1.

The sharp-eyed among you will see at once that important thing 1 is really the same thing as important thing 3.

I realize that this method may take a little longer than actually multiplying, but for those of you who dislike multiplying or never managed to memorize the multiplication tables, you now have an alternate way to determine the answers to multiplication problems.

In other words, if time is not of the essence, you're in like Flynn.