Introduction: How to Multiply
Today you'll learn how to multiply big, huge numbers just knowing how to count, and add.
This system is as easy that any kid should learn it, because it's totally graphical. So, let's go!
*EDIT: Thanks to mrmucox for noticing about the formatting problem, now it's solved ;)
Step 1: Drawing the First Number
Ok, let's say we want to multiply 37 * 51. We all know that if we take our calculator, and multiply, we'll get 1887. Now, we'll forget about using calculators, and we'll take a notebook and some pens. So, our first number is 37. As its first digit is 3, we'll draw 3 diagonal straight lines (from the left-lower corner, to the right upper corner). Now, we'll draw 7 lines (for the second digit, a 7), a little bit below the first ones (look at the pictures).
Step 2: Drawing the Second Number
Now, we'll draw the second number, 51. First, we'll draw five straight lines (for the first digit, again) crossing the lines from the first step, and placed as down as you can (but always crossing the other lines). Then, we'll draw the lines for the second number (1) a little upper.
Step 3: Adding Up
Now, you need to pay a little more attention. Once you have all the lines drawn, you'll have to group the cross that got made, and add them up. How do we do that? Grouping them from up to down. I know it isn't quite clear, but look at the images and you'll understand ;)
So, we got the first group, containing 15 crosses; the second one, with 38 crosses, and the last one, with 7 crosses.
Now, we write this numbers down:
*(Why do we put the 3 in 38 below the 5 in 15? Because it's a two digit number. If the sum results are only one-digit numbers, we'll set them apart, as I did with the 7)
And... that's it! We got the result we were looking for, 1887!
Step 4: Another Example
Well, I'm working faster, just one drawing per example will be enough. So, what happens with bigger numbers? Let's try it out with three-digit numbers, in example, 314 * 261. Just look at the pictures to see how we do the pattern, and then the adding up. The final add will be this way:
As you can confirm, 81954 is the result of multiplying 314 * 261 ;)
Step 5: Ask for Help, and Keep Practicing
Well, we're ready here. If you have some troubles with this Instructable, you want to share your own examples, or want to make it better, just leave me a message ;) And don't forget, that practicing is the best way to learn all of the life's tricks ;)