Addition and Subtraction
Adding Two- and Three-Digit Numbers
Solving Stacked Addition Problems
To solve stacked addition problems, all you need are the skills you learned in Lesson 1.
Let's try solving this problem, 24 + 12.
To solve a stacked addition problem, start by adding the digits farthest to the right.
In this case, that means we'll add 4 and 2.
Like with any addition problem, we can use counting to help us add. Since our first digit is 4, we'll start with four objects.
We're adding 4 to 2, so we'll use two more objects.
We can count to get a total of 6. We know that 4 + 2 = 6.
Write 6 under the line. It's important to put it directly beneath the numbers we just added.
Next, we'll add the digits to the left of the ones we just added. That's 2 and 1.
We'll use two objects to show the 2.
Next, we'll add one object to represent the 1.
When we count, we get 3.
We'll write the 3 under the line, beneath the 2 and 1.
We're done! Our total is 36, or thirty-six.
Let's look at one more problem, just for practice. This time, we'll solve 62 + 5.
We'll start by adding the digits on the right, 2 and 5.
2 + 5 is 7.
Now, let's add the digits to the left. The top digit is 6, but there's nothing beneath it.
6 plus nothing is 6, so we'll write a 6 below the line.
Our total is 67, or sixty-seven.
As you saw, stacked addition problems are always solved from right to left. This means that you always start by adding the digits on the right.
Try it! Solve these stacked addition problems. For now, just type 0 in the box that appears above the numbers on the right.
Adding Very Large Numbers
Stacked addition can also be used for adding larger numbers. No matter how many digits are in the numbers you're adding, you add them the same way: from right to left.
Let's try adding two 3-digit numbers. We'll complete this expression: 213 + 406.
As always, we start with the digits on the far right. Here, that means we'll solve 3 + 6.
3 + 6 is 9, so we'll write 9 directly beneath the 3 and 6.
Next, we'll add the digits to the left of the ones we just added, 1 and 0.
1 + 0 is 1, so we'll write 1 below the line. Make sure to put it directly beneath the digits we just added, to the left of the 9.
Finally, let's add the next set of digits, 2 and 4.
2 + 4 is 6. Let's write the 6 beneath the line, under the 2 and 4.
The problem is complete. Our total is 619, or six hundred and nineteen. 213 + 406 = 619.
Now you try it. Add these large numbers. Again, just type 0 in the boxes that appear above the problem.
