Speaker (woman):

We have been working to add three-digit numbers – both with our base-ten blocks and when writing out the problem like this.

On-screen: [(Problem is presented vertically): 273 + 152.]

But I've noticed that some of us are having trouble with adding when we need to regroup or make trades. So today I am going to show you how to do this addition problem, 273 plus 152, using base-ten blocks to help us understand what each of the numbers we are recording means. Our blocks will help show us when we regroup, and we will be able to see what is happening at each step when we solve an addition problem like this.

Remember, we have used base-ten blocks before. This is a flat. It is worth a hundred. This is a rod. It is worth ten; and, remember, ten rods are equal to one flat. This is a small cube. Small cubes are worth one; and ten small cubes are equal to one rod.

On-screen: [Screen shows two flats (100 each) worth 200; 7 rods (10 each) worth 70; 3 small cubes worth 3.]

So, when we do an addition problem using the base-ten blocks, the first thing we need to do is build the first number. In this case, our first number is 273. I'll start with the hundreds, and because I have two hundred, I will take two flats. I will have 100, 200. Next, I need seven rods because there are 7 tens or seventy. This makes 210, 220, 230, 240, 250, 260, 270. And, finally, I need three small cubes because I have three ones. And that will give me 271, 272, 273. So, that's our first step. We have made the first number, 273.