Pre Algebra Multiplying Large Numbers

Sometimes we have even bigger numbers to multiply together.

It still works mostly the same way:

Example:

We start out the same way as before.

First Multiply 4 x 6.
4 + 4 + 4 + 4 + 4 + 4 = 24.
Write down the 4.
Put the 2 at the top of the next column.

Now Multiply 4 x 3 and add the 2.
4 + 4 + 4 = 12.
12 + 2 = 14.
Write down the 4.
If there were more columns
we would write the 1 on the top and go on.
Since there are no more columns,
we write down the 1 too and we're done

So now we're done with the 4.

We still have the 1 in the tens column to deal with.

We will multiply it times each of the numbers on top next

but with one change.

The 1 we will multiply by is in the tens column.

So we start writing the answer numbers in the tens column too.

So that the numbers stay lined up right,

we put a zero for a place holder in the first column.

(Hey, being a place holder is what zeros do best)

Put a 0 at the bottom of the first column
as a place holder.

Now Multiply 1 x 6.
1 + 1 + 1 + 1 + 1 + 1 = 6
Write down the 6.

Now Multiply 1 x 3.
1 + 1 + 1 = 3
Write down the 3.
Now we're out of numbers so
We're done with this part,
but there's still one more step to go.
We need to add together the two numbers
that are below the line.

Add the two numbers.

4 + 0 = 4. Write down the 4.

4 + 6 = 10. Write down the 0 and put the 1 on top of the next column.

1 + 1 + 3 = 5. Write down the 5

and we're done.

Let's try another one ...

Example:

We start out the same way as before.

First Multiply 7 x 6.
7 + 7 + 7 + 7 + 7 + 7 = 42.
Write down the 2 and put the 4
at the top of the next column.

Now Multiply 7 x 5 and add the 4.
7 + 7 + 7 + 7 + 7 = 35.
35 + 4 = 39.
Write down the 9.
If there were more columns
we would write the 3 on the top and go on.
Since there are no more columns,
we write down the 3 too.

So now we're done with the 7.

We still have the 3 in the tens column to deal with.

We multiply it times each number on top.

Since the 3 is one column over in the tens column,

we put a zero on the bottom in the ones column as a place holder.

Put a 0 at the bottom of the first column
as a place holder.

Now Multiply 3 x 6.
3 + 3 + 3 + 3 + 3 + 3 = 18.
Write down the 8 and put the 1 at the top of the next column.

Now multiply 3 x 5 and add the 1.
3 + 3 + 3 + 3 + 3 = 15.
15 + 1 = 16.

Write down the 6.
Since there are no more number columns, we can write down the 1 too.

Add the two numbers.

2 + 0 = 2. Write down the 2.

9 + 8 = 17. Write down the 7 and put the 1 on top of the next column.

1 + 3 + 6 = 10. Write down the 0 and put the 1 at the top of the next column.

1 + 1 = 2. Write down the 2.
We're out of numbers so we're done.