Multiplication 7: Old video giving more examples

2 examples of multiplying a 3 digit number times a 2 digit number. 1 example of multiplying a 3 digit number times a 3 digit number.

Welcome to Level Four multiplication.

Let's do some problems.

Let's say we had two hundred thirty-five times--

I'm going to use two different colors here, so bear with me a second.

Let's say times forty-seven.

So you start a Level four problem

just like you would normally do a Level Three problem.

We'll take that seven, and we'll multiply it by two hundred thirty-five.

So seven times five is thirty-five.

Seven times three is twenty-one, plus the three we just carried is twenty-four.

Seven times two is fourteen, plus the two we just carried.

This is sixteen.

So we're done with the seven.

Now we have to deal with this four.

Well, since that four is in the tens place, we add a zero here.

You could almost view it as we're multiplying two hundred thirty-five, not by four,

but we're multiplying it by forty,

and that's why we put that zero there.

But once you put the zero there, you can treat it just like a four.

So you say four times five, well, that's twenty.

Let's ignore what we had from before.

Four times three is twelve, plus the two we just carried, which is fourteen.

Four times two is eight, plus the one we just carried, so that's nine.

And now we just add up everything.

Five plus zero is five, four plus zero is four, six plus four is ten, carry the one,

and one plus one plus nine, well, that's eleven.

So the answer is eleven thousand forty-five.

Let's do another problem.

Let's say I had eight hundred seventy-three times--

and I'm making these numbers up on the fly, so bear with me--

eight hundred seventy-three times-- some high numbers--

ninety-- and I'm doing them in different colors,

just so you hopefully get a better understanding

of what I'm trying to explain.

Let's say ninety-seven.

No, I just used a seven.

Let's make it ninety-eight.

So just like we did before, we go to the ones place first,

and that's where that eight is,

and we multiply that eight times eight hundred seventy-three.

So eight times three is twenty-four, carry the two.

Eight times seven is fifty-six, plus two is fifty-eight, carry the five.

Eight times eight is sixty-four, plus the five we just carried.

That's sixty-nine.

We're done with the eight.

Now we have to multiply the nine,

or we could just do it as we're multiplying eight hundred seventy-three by ninety.

But multiplying something by ninety is just the same thing

as multiplying something by nine and then adding a zero at the end.

So that's why I put a zero right here.

Let's say nine times three--

well, first, just to clean up things, let's get rid of what we had from before.

We say nine times three is twenty-seven, carry the two.

Nine times seven is sixty-three, plus the two that we just carried is sixty-five.

Carry the six.

Nine times eight is seventy-two, plus the six we just carried.

That's seventy-eight.

And now we just add again.

Four, eight plus seven is fifteen, one plus nine plus five is fifteen,

one plus six plus eight is also fifteen, and one plus seven, that's eight.

So the answer, hopefully-- I don't have a calculator in front of me--

is eighty-five thousand five hundred fifty-four,

assuming I didn't make any careless mistakes.

Let's do one more problem.

I think it'll hit the point home.

The next problem I'm going to do,

you can almost do it as a Level Five problem

because I'm actually going to multiply two three-digit numbers,

but it's really the same thing, and hopefully, you'll see the pattern.

So let's say I had two hundred thirty-four times--

and I'm going to use three colors now--

let's say six hundred forty-three.

So first we do the three, which is in the ones place,

and we multiply that times two hundred thirty-four.

Well, three times four is twelve, carry the one.

Three times three is nine, add the one.

That's ten, carry the one.

Three times two is six, plus one.

Well, that's seven.

And then we've done the--

I think I've made a mistake someplace.

Let me see.

Three times four is twelve.

Oh, no, I think that's correct.

I was confusing myself.

Okay, now we're ready to do the four, or the forty,

and since it's a forty, because it's in the tens place, we put a zero right here.

We say four times four--

well let's clean up the stuff at the top.

I always forget to do that.

Four times four, well, that's sixteen, carry the one.

Four times three, well that's twelve, plus one, well that's thirteen.

Four times two is eight, plus the one, well that's nine.

And now we're done with the four, or the forty,

depending on how you want to view it.

Now we're ready for the six, or the six hundred.

Since it's a six hundred, we put two zeros here,

and we just treat it like a six.

Let's clean up what we did before.

So six times four is twenty-four, carry the two.

Six times three is eighteen, plus two is twenty, carry the two.

Six times two is twelve, plus two is fourteen.

And now we add it all up.

Two. Six. Seven plus three is ten.

Fourteen, carry the one.

One plus nine is ten.

Carry the one.

That's five, that's one.

I hope you can see. I hope it's not falling off the screen,

the answer I get is a one hundred fifty thousand four hundred sixty-two.

I think you're ready now to try Level Four multiplication problems!