Introduction: How to Multiply
Hello! If you are reading this I am assuming that you need some help doing some multiplication.
Multiplication is a very important skill that most everyone needs to function in normal society, weather your doing your budget, or calculating costs for your projects, it's essential to know how to multiply. Remember, you can't always have a calculator by your side.
Let the multiplication begin!
Step 1: What Is Multiplication?
At it's very basics, multiplication is just repeated addition. what does that mean? well let's take a look.
lets use the problem 5x4. we can get the answer by using multiplication (or repeated addition). so we can get the answer by adding 5 to itself 4 times. it looks like this;
5+5+5+5 and we get 20! so 5+5+5+5=5x4
or if you would like to see a visual, you can make a grid. so for our problem, it would be a grid of four columns, with five rows, and you can see that we have twenty dots!
Now you could just do multiplication that way, but when you use higher numbers it would take forever! so there are methods that make multiplication quick and easy, and all based on that same idea!
Step 2: Multiply With Larger Numbers Using Lattice
There are so many different ways to multiply, but the truth is, you only need one good one. And the lattice method is by far the easiest.
The lattice method of multiplication only requires that you be able to do multiplication up to 9x9, and that you can add single digit numbers.
Step 3: Setup
we are going to do a simple problem, a one digit number, multiplied by another one digit number.
first you need to draw a cube, then draw straight a line stretching from the top right corner, to the bottom left one. then write the first number on top, and then the second number on the right.
as you can see in the picture, there is a place for the tens on top, and a place for the ones on bottom.
Step 4: Multiply
okay, we are going to use the problem 7x3=21. you have to remember that 20 is the tens place, and that 1 goes in the ones place. plug that into our little cube that we drew earlier. do this a couple times to get used to it.
Step 5: More Complicated Setup
alright, up until now you have just been doing simple 1x1 lattices, and you can see the results, but what would happen if you used a 2x1 lattice, and a little addition? well, lets take a look.
well first, you are going to set it up a little differently. take two of those cubes and put them next to each other. then on the top you are going to write your two digit number. then on the right, you write your one digit number.
after you have done that, you can begin to solve
Step 6: Solve It
alright, now what you have to do is imagine all of the numbers on the top have an invisible line attached to them going vertically, now imagine that the numbers on the sides have the same invisible line attached to them, but going horizontally.
all of the invisible lines will intersect inside of a cube, then take the numbers that have intersected and multiply them. write them into your cube, remembering where your tens and ones places are.
lets take the problem 12x3. 12 would be on the top and 3 would be on the side. you would take the cube where 1 and 3 intersected and write in 0 for the tens place, and 3 for the ones place, because 1x3=3. then you would do the same thing with the cube where 3 and 2 intersected, writing in 0 and 6.
Step 7: Solve It (part 2)
all right, now you should have a whole bunch of cubes, and a whole lot of numbers filled in. so what do you do with them? well remember those diagonal lines that we drew earlier, well they were there for a reason.
you take all of the numbers in between the two most right diagonal lines and add them together. then write the number in the space below where the two lines end. do that with all of the groups of diagonal numbers. if you get a number bigger than 9 you take the tens value and put it in the group of numbers to the left of it.
then you get your answer by reading down the left side and across the bottom and we learn that 3x12=36!
Step 8: Your Done!
this method can be used for any multiplication problem, you just increase the size of the grid, and follow the steps in the exact same way. remember, practice makes perfect! after doing a few of these you will be doing multiplication like a professional mathematician!
here in the picture, there is an example