How to Multiply

by ratolibre1

4.9K218

Intro: 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:

15
038
0007
____
1887

*(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:

6
20
017
0025
00004
_
81954

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 ;)

12 Comments

Spypro 14 years ago

I have some interesanting thing to do with these system, to work with tose hudge numbers, but mentally and the limit is actually the efficency of persons immaganative cortex, so if you are interesated?

genknight 15 years ago

its nice but I don't think its so practical since the normal way is actually doing that what you do here. besides , drawing those lines is more time consuming too. all the kid needs to do is learn the multiplication table up to 9 and be able to add. this is nice in the beginning to learn the multiplication table but it shouldn't be used too often cause then it'll be a crutch later on.

37
x 51
7 (1x7=7)
3 (1x3=3)
35 (5x7=35)
+ 15 (5x3=15)
1887

genknight 15 years ago

drat , i lost the formatting

zemalc01 15 years ago

What about zero's? Do you just add in a line that's all 000000's?

The Dark Ninja 15 years ago

I agree, can you provide some info on how to multiply numbers like 30*27?

naught101 15 years ago

why do you add the 0s on the start of the lower numbers (038 and 0007 in the example)? It would make more mathematical sense to add them to the end of the higher numbers (to get the monospace formatting, use {{{ on the line before, and }}} on the line after the stuff you want monospaced):
1500 380   7+

cutting Matt 15 years ago

why don't my teachers teach me this? i could just sit at home reading instructables instead of going to school!

mrmucox 15 years ago

I think you lost some formatting on steps 3 and 4. Instructables removes multiple spaces. I think you meant

15
038
0007
1887

AND

6
20
017
0025
00004
81954

ratolibre1 15 years ago

Thanks! I edited it as soon as I read your comment. Didn't notice about the problem ;)

nagutron 15 years ago

Word. That is much clearer, mrmucox.