Look at how Emma broke apart a number to help her add. 319 plus 400 equals what? First, add the hundreds. 300 plus 400 equals what? Then add the hundreds to 19 to find the total.
We can see that Emma wants to find the answer to 319 plus 400. But look at what she’s done. She’s turned the calculation into a part-whole diagram. Underneath the number 319, she’s broken it apart into 19 and 300. Why has she done this?
Well, we know that the number 319 is made up of three hundreds, one ten, and nine ones. And the number that Emma needs to add to this three-digit number is a number of hundreds, four hundreds. So to make things easier, Emma has broken apart 319 so that she can add the hundreds. That’s why, on one side of her part-whole diagram, she has the number 300. And on the other side is the rest of the number, 19.
In the first part of the problem then, we’re asked to add the hundreds, 300 plus the 400 that we need to add on. Well, we know that three plus four equals seven. So 300 plus 400 must equal 700. Let’s count in hundreds to see if we’re right. 300, 400, 500, 600, 700. 300 plus 400 equals 700.
Now we still haven’t found the answer to our problem. Our number is still broken apart. We still have a number of hundreds, which has now changed to 700, and then the rest of our number, which we said was 19. We need to combine these two parts back together again. In other words, we need to add the hundreds to 19 to find the total. 19 plus 700 equals 719. And so if we add four more hundreds to 319, we get the answer 719.
We found the answer by first adding the hundreds. 300 plus 400 equals 700. Then we added the hundreds to 19 to find the total. 19 plus 700 gives us a total of 719. The answer to Emma’s calculation is 719.